I'd make sure he has a clock or similar so that he can SEE when it is night time and when it is morning. And then be very very clear about the rules. When it is night time, it is sleep time. Mummies needs sleep and so do boys, so there is going to be no more getting up in the night. You could give him three 'tokens' for three callbacks, and once those are done, they are done.
I would also role play with him what to do if he wakes up in the night - yawn, roll over, cuddle teddy, close eyes and go back to sleep. If he needs to pee, he can get up and do that by himself, he doesn't need you.
At bedtime, make sure he has everything you can think of - make sure teddy is near by, there is a drink of water on his nightstand, he has been to pee - and after that I would do the Supernanny 'silent return' thing.
That means, the first time he comes out to you, you take him by the hand and take him back to bed saying "it's bedtime darling."
The second time, you take him back to bed saying, "bedtime".
Every subsequent time he comes out to you, you just take him back to bed without saying a word. And keep doing that for as long as it takes until he stays in his bed. Be prepared to get NO sleep the first night, but it should get better pretty quickly once he knows you mean business.
