M.B.
Unfortunately you may have to just take it away entirely! When he asks for the bottle, tell him they are all gone because big boys don't need bottles. Make a big deal about the fact that he is such a big boy that he only can only use his cup! Show him how his sisters use only cups, and maybe they can help make the super big deal!
Then when he asks again, just tell him again. It may be tough for a couple days, but hopefully he will stop asking! Good luck, I know it will probably be harder for you than for him! :)