Hello M.!
I have a two and a half year old son, and about 18 months of age he wanted to take his cup to bed with him. I had no problem with it, other than your concern, and that was the fact that I was worried about his teeth. I think it's completely fine to give him the cup when he goes to bed. I understand that he's not drinking water, but no matter what you do, there is going to be a battle. Might as well choose which one you'd prefer, the one where he's upset over the water for 5 minutes, or the one that will continue to wake you up every night. My son stopped asking for his cup when he became potty trained, and the wonderful thing about it is in the morning the cup is not empty. I don't think it's fair to completely deprive him of the cup, and it's not fair that you're in the position where you have to get up with him either. Have you ever woke up in the middle of the night, after sleeping so soundly, and your mouth is COMPLETELY dry? I am sure that this is what's happening to him. I would suggest you battle for water, but understand in the long run that he's not going to damage his teeth, because he won't be sucking on the thing all night long, and you're not going to be a zombie because you played waitress the night before. It will be much easier on everyone to persuade the beverage option, than to quit the entire thing all together. Make sure to wash out the cup every morning, as the saliva that builds up inside the cup can cause some yucky bacteria to take shelter in your little man's cup! Best of luck with everything honey, and I hope that whatever you choose to do works out well for both of you :)
Peace, Patience and Prosperity,
H.