E., Years ago, Mom told us how she broke my brother and sister of their bottles. I know it's not the same, but it may help.
Brother used glass bottles (kinda hints at his age, doesn't it??) and he had a habit of grabbing the nipple and dragging it along the crib when it was empty then THROWING it across the room. Mom gave him the last one and TOLD him it was the last. NO MORE. When he thru that one, she just shrugged and said, oh well. He never asked for it again.
Sister simply got too old for it. Mom put her down for her nap and she asked for her bot. Mom made up this story about a momma dog came around and needed it for her puppies. Sister said Puppies? Yes, puppies. She rolled over and went to sleep. That night, she asked for her bot. Mom said, the puppies have it. Puppies? yes, puppies. She asked one more time and that was it. She never asked again.
The key is being insistent and not giving in. Shut the door. Let him cry. (It won't do him any permanent harm.) Check on him every five minutes or so. Let him know that you are still there. But DON'T give him the cup. Make sure he has a drink before bed and leaves the cup in the sink. Not to be touched again. Then off to bed.
There may be crying for a while, a few days maybe even. Eventually, he will realize that you will not be giving it back to him and he will go to sleep.
It won't be easy. But the question is, when you finally put him to bed and he curls up with his teddy bear (that is a must for every little one, ya know) and goes right off to sleep, will it be worth it all? I think you will say yes, it was worth it all.