Maureen how old is Jamie?
When I stopped the night feeds with my son it wasn't easy. He'd keep signing for milk and I'd just say "no" to him, offer him water and hold him. He'd cry and keep signing for milk. I'd just acknowledge that he was asking for milk and tell him that I am sorry but I only have water and that he can't have milk now. They understand a lot more than we think - so tell them what you are doing. I'd also tell Dieter that I was not going to give him milk during the night anymore. It wasn't nice but something that needed to be done. It was a comfort thing. But it is only a few difficult nights. So byt net vas. When Jamie asks for bottle, just offer him bottle with water instead.
I don't have experience with bottle as I am breastfeeding but read on Mommalicious group on FB that few ladies said to take your time with taking bottle away as they are only small for X amount of time. But again, you as his mom knows best so follow your instinct and heart. What does the kids as his school use? Perhaps the teacher can help like you said by encouraging him to do what the other kids are doing? Or are they all on bottle with milk?
In the end it is just to persevere and not give in.
Here are the different cups Dieter drinks from.
The straw cup thingy has a rubber straw which is very soft and easy to drink from. bought at Reggies for R20 or R30.
The sippy cup with the orange lid is a cheap cup which doesn't leak and you can buy it from The Crazy Store for cheap (R20 or less). Brandname Chooey with picture of orange lion on it.
I bought a real mug (Winnie the Pooh) for Dieter and he drinks his tea from it in the afternoons (and messes half of it) but he is so chuffed to be drinking from a mug the way we do. They love to copy. So I would have a mug of tea with him when he has his. I also keep a dishcloth handy, ha ha.
The red plastic mug I bought for less than R20 for a set of 4 (different colours). I sometimes give him otees in it as a snack and other times a mouthful of water in it or juice for him to practice drinking from. Always messy but again he likes the "grown up" thing I guess

The blue Winnie the Pooh bottle is very hard but he manages to drink water from that too. I don't offer it often but he drinks from it.
Maybe this helps you with a few alternatives for substituting Jamie's bottle? Maybe take Jamie to the shops and let him pick a "big boy cup" to drink from?
Good luck. I must start weaning Dieter off the boob and put him in his own bed and I have four months left