S.L.
Have you seen the transitional cups that have two handles and a bottle-like silicone nipple that you can switch to a few different other styles of spill-proof silicone sippy things. That probably made no sense whatsoever. But that way, it's the same cup, with his favorite two handles, and then it gradually moves them from nipple to sippy cup shape.
I saw them at WalMart tonight, although I have to admit that I haven't had the need to really look into all the features. I'd hate to mislead you!
You could also forget the sippy cup and move him straight to a regular cup. But that sounds like a horrid idea to me, personally. My oldest is 4, and despite my desire to switch to a normal cup, I REALLY like not worrying about spills!
Good luck,