I went bowling with some friends the other day. I do not own a ball and used the balls that were available there. One frame I knocked down 9 pins. So, I took a light ball, and very slowly tossed said ball down the alley earning the spare. I did not put my fingers in the holes (I see the sexual connotations coming so please spare me), and yes, I did pull somewhat of a spread leg granny roll, I did not run to the pins, just walked up and let the slow roll begin.
My friends laughed and called it a foul. If (I wish) lived in the Big Lebowski universe, would Walter (John Goodman) pull a piece on me and call me Smokey?
Walt may pull a piece on you anyway (his buddies didn’t die face-down in the mud in 'nam so people could granny roll, after all), but I’m not sure what ‘legal’ basis he’d have. For a skilled bowler, I’d imagine the standard form gives more control than granny rolling. Standard certainly gives more power, so I don’t think granny rolling could be banned for giving an unfair advantage. Strictly IMHO, but as long as you stay behind the foul line, it should count.
While granny rolling isn’t specifically mentioned, you used both hands instead of your usual one-hand delivery, so technically, if you didn’t get your friends’ permission beforehand, your total score should have been zero.
Any friends who would score you a zero on that are just being asses. It is true that your delivery must at least stay with the same hand during a game (or match) for league purposes. This is to prevent people switching hands to make a 7 or 10 spare easier on themselves, and other things, I’m sure.