Titan, do you think your son could handle small amounts of milk in a cup with no top? I noticed that my babies all do the same thing with sippy cups - throw them. Especially with milk. I finally had this brain blast and realized that they were annoyed with trying to quench thirst through the little holes. I took the top off and gave them about an inch of liquid, helping them hold it at first, of course, and voila! No more sippy cup woes.
If he's recently off formula (though at 2, I don't see that being the problem) then maybe half formula and half milk would help him adjust? Or you could just ditch the bottles, like others have suggested. Instead of a transition just make them mysteriously disappear.
Another idea might be to try those sports cups with straws. The kind that flick open prevent spills, but any sort will work. My 6yr old was especially attached to his bottles and two before he was willing to give them up - the straw cups helped him transition better than sippy cups did. Good luck!
