My wife tells me when she was a kid, on one trip the family car had only one tape in it. It was Briefcase.
After about the third time Rubber Biscuit came on, her mom punched the eject button and tossed it out the window. 
I misunderstood gimmick. I was going to say A Kind of Magic by Queen. I’m pretty clueless musically, but I hadn’t seen a band release an album that was basically just a movie soundtrack. It was cool and kind of gimmicky to me.
And it is amazing.
It is amazing.
I still love Grunt by Sandra Boynton – yes, that Sandra Boynton, who used to do all the cutesy punning greeting cards and the children’s Board books.
Grunt is a parody of the inexplicably one-time oddly popular album Chant , featuring the monks of Santo Domingo de Silos performing Gregorian chants:
Boynton’s album is “Pigorian” chant, but it’s much more than a one-joke album. This is evidently a twisted labor of love. If you put it on in the background, the unwary won’t even recognize it as a parody – it sounds like real Gregorian chant. Until, that is, you listen really closely, or peruse the lyrics sheet. It’s a weird mix of real Latin lyrics (but not to traditional chants, being things like “Old MacDonald Had a Farm” translated into Latin), Pig Latin (“Ore-snay!”) and atrocious puns (“Gloria to Egg Shells each day-o”)
Definitely worth picking up.
A friend of mine says the BB Band was essentially the MG’s without Booker T.
Well… and without Otis Redding, and Sam & Dave, and Rufus Thomas, and …
Along vaguely similar lines - the deceased Elvis makes new musical friends (also deceased, obviously) and is then reincarnated in the form of Belfast postman James “The King” Brown, to create a new album (Gravelands) featuring songs by his new friends. Come As You Are, Love Will Tear Us Apart, Somethin’ Else (twice, kinda) and so on.
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I had considered mentioning Big Daddy, as well. 
A couple of my favorite examples:
“Nothing Compares 2 U” done in the style of Little Richard.
“Money For Nothing” done in the style of Tennessee Ernie Ford’s “Sixteen Tons.”
Fans of Big Daddy and Dread Zeppelin should check out Richard Cheese. He covers songs in a lounge style. Here’s his version of Gin and Juice and Welcome to the Jungle.
Jethro Tull’s Aqualung album was regarded by many critics as a concept album due to there being a distinct theme to each of the two sides of the album. Ian Anderson disagreed with these themes being strong enough to be called a “concept album”, and so for Tull’s next album set out to create the ultimate concept album: Thick as a Brick. Over-the-top gobbledygook lyrics meandering all over the place while seeming to be serious, mixed with some passages of complete nonsense (“We walked through the maternity ward and saw 319 BABIES WEARING NYLONS”), all wrapped together in one continuous (save for flipping the album over) 45 minute piece of music. They took it even further by making an overly elaborate gag newspaper to serve as the album cover and liner notes, filled with all sort of ridiculousness that one might find in a small-town newspaper but taken to a more extreme level, led by the cover claiming that the lyrics to the piece had been written by a 12-year-old boy and were entered into a poetry contest that he was disqualified from in a “last minute rumpus”.
It’s probably my favorite Tull album, precisely because it doesn’t try to hide their pretentiousness at all. It fully basks in its glory, and it’s magnificent.
If not the music, even the newspaper would be enough to attain “gimmick” status. And like the National Lampoon newspaper & yearbook parodies, a thorough reading yields so much interlocked detail.
Oh, look, you can read the entire St. Cleve Chronicle… I have friends that allude to it, referring to someone as an “alleged Hell’s Angel” or replying to a non-sequiter with “Hello, who’s Fluffy the Duck talking to this week?” (see the Family Fun Pages, you’ll be glad you did)
And speaking of Aqualung, as a kid I spent an entire eight bucks on a Tull ticket, before anyone even knew there’d be a new album that the lads were trying out. They broke right into the entire Aqualung album, and it was mind-blowing.
Got my middle-aged mind blown by walking past the same theater a while ago: “Aqualung, 40th Anniversary Concert”, for only 10x what I’d paid the first time.
“Your Axed for It” and “Heterosexuals Have the Right to Rock” by the Mentors.
Anything by Steel Panther.
That would be Blue Lou Marini which I remember because I can still hear Jake introduce the band on one of their live albums that I owned. Weird thing to stick in memory but I loved that album and the band as well.
I’ve said it before – my favorite Big Daddy piece is their cover of Celine Dion’s My Heart Will Go On from Titanic. They take that ethereal, heartbreaking song and turn it into a happy bouncy Elvis Presley song so far removed from the original that at first I had no idea what song it was. It’s hilarious - especially when you place close attention to what the chorus is singing in the background.
The Original Concept Recording of Jesus Christ Superstar was considered a gimmick album: Two unknown Brits write a “rock opera” about the last week of Jesus’s life, only from Judas’s point of view, and manage to get it recorded and distributed in England, where it fails to go anywhere.
I’m gonna nominate the Beethoven’s Wig albums, which add lyrics to a bunch of classical music’s greatest hits. Some of my favorites:
Please Don’t Play Your Violin At Night (to Eine Kleine Nachtmusik)
It’s the Same Every Verse (to In the Hall of the Mountain King)
Please Keep Your Bull Outside the China Shop (to the Toreador Song from Carmen)
Sing Verdi Very Loud (to La donna e mobile from Rigoletto)
I Want My Diploma (best use of Pomp and Circumstance ever!)
They did a similar job on Memory (from “Cats”).
Well if we’re calling Shatner’s “Has Been” a gimmick album…Loungeapalooza has some fantastic tracks on it.
It contains a Spinal Tap reference. Which is unusual because it was released twelve years before the movie.
Rufus? He’s the man.
Just to nitpick the OP a bit, Murphy Dunne and Willie Hall were not part of the original Blues Brothers band on SNL or on the Briefcase Full of Blues album. Paul Shaffer and Steve Jordan were the original keyboard player and drummer. Dunne and Hall replaced them in the movie for… contractual reasons?