There is a pretty good precedent for USMC helo pilots doing interservice transfer to USAF.
If I were you, I would get an one on one interview with a USAF operational commander in a coomand that has a lot of USAF helicopter assets - a great example might be the 1st Special Operations Wing down at Hurlburt Field. Get a 45 minute appointment with him, fly down there, get your intentions known, why you want to do an interservice transfer, etc.
Do all your homework first obviously - but once you have your facts dpwn and you know this is something you want to pursue, then make a few phone calls, write a letter, get some face time, and then fiure out how to let USMC release you...
Totally doable in my opinion.