Get a tattoo.
I do the same thing, and it helps tremendously. Except I say sep-AH-rate when I’m typing it, and it’s never leaked into normal conversation–unlike, say, hyper-bowl.
Great minds must think (or misspell) alike, because separate is a word I always used to misspell.
What’s strange is that one would expect to eventually remember the correct spelling! No: One remembers that one has trouble with the spelling and some Imp of the Perverse insists on continually misspelling it.
Here’s what finally worked for me. A distinguished scientist was invited to hear my invention idea and I eagerly awaited his feedback. His first comment? “seperable is misspelled.” :smack:
I don’t think I ever misspelled it again after that.
I was taught to picture a hillbillly – call him “Sep” – listening as his shrieking wife sees a rat scurry across the floor. “Sep! A rat! E!”
I misspelled it on a 9th grade history test. I had to write it 20 times on the back of my paper.
Have not made the mistake again. 
This works best.
For some reason, it’s the actual Latin word parare that has stuck in my mind, which does the trick.
I have the same problem.
Looking at the OP, it occurred to me the best bet is probably going to try to remember it is Sepa Rate. Break into two words, remember the first is Sepa.
By next week I’ll be spelling it as Sepahrate. 
Me too. Every time I write it I hear see Pa rate in my head.
I also do the exaggerated “seh-PAH-Rate” sounding-it-out thing.
Another suggestion for this one might be this: every vowel that could be an “a”, is. That is, max out the number of “a”'s. (This is similar to how I remember “Tennessee” and “committee”… just double every letter that is even remotely double-able.)
I think of “pare,” like BDoors mentioned above. But, when this was a spelling word for my third grader, we made up a silly sentence:
Seven Elderly Pigs Are Running Around The Elephant
There was a poster in my elementary school classroom that read…as best I can type:
“sepArate”. The “A” was drawn as a mountain…with snow on the top, etc. It was a simple visual mnemonic devise that showed a physical separation of the word via the mountian of the “A”. As a visual guy I find it easier than remembering where rats are located.
I’m another rat speller. There’s a rat in the middle.
I don’t think I’ve ever written the word “separate” without first reciting “there’s a rat in separate.” As soon as I saw the thread title I said, “there’s a rat!”
I also have to say “Tom or row” and “Be uh you tiful” to write those words.
Bad advice. I would end up spelling it se pare te. 
mmm
How about “If you separate the parts, each part will be on a par with the other?”
I think of the middle “part.”
“Two E’s separated by two A’s”
Does that help?