Ok, I know this sounds silly, but are you sure he's biting? I was convinced my DD was biting, and after checking for teeth marks, realized it just FELT that way because of the pregnancy/hormonal pain associated with nursing.
If you're absolutely positive (teeth marks and all) that he's biting, I'd agree - maybe the flow isn't as fast as it used to be. Maybe you can try hand expressing into his mouth a bit while he nurses? Can you look for signs that he's about to bite so you can stop it before it starts? If not, I'd continue doing what you're doing - he will eventually realize that unless he stops, he won't get the milkies.
FX for you!