Hi C.,
I too have heard this before from my baby girls!! (10 & 4 now)
The best cure I know is this......fill the bottle w/ something boring like water or a beverage he doesn't like, fill the sippy cup w/ the absolute favorite drink and let him make a choice. It kind of gives him the sense of making his own decision and not doing what mommy wants at all!! Just leave the choice up to him! Set it on the table explain he has a choice, but don't refill the bottle, leave the cup full & in sight. The key to this trick is to STICK TO YOUR GUNS, always fill the bottle w/ not so good and the cup with the favorite! After time even if he chooses the bottle keep filling it less and less, but make sure the cup is always full, when he starts to choose the cup more often then not, hide the bottle! It may take a week but if you don't make a fuss over it eventually he should be weened!! GOOD LUCK
K.