I think part of the problem with advancing the internal portion of the corpus cavernosum (I believe the female equivalent is the crura) would be nerve or blood vessel damage. Those structures probably aren't naturally free to move forward and the free-up may carry a risk of nerve damage that would compromise erogenous sensation.
I've heard mention of 'advancing the crura' as a surgical technique, but I haven't heard any recent talk and (to my knowledge) none of the surgeons that I was considering offered it. Beyond that, I dunno. If you're really interested in having this done, it would probably be best to consult a bottom surgeon.