J.,
Our son is six and has tried this numerous times in the past. We have a standing rule that he is only allowed to get out of bed two times. (Unless it is a real emergency) He can either go potty, get a drink, or ask a very quick question. After his second time he gets a swat and is sent back to bed.
He knows the rules and accepts the consequences when he breaks the rules.
You might want to think about putting your son into a pull up diaper for bedtime. Then if he has an accident it is contained. This way you can set your own rules and have a back-up for potential accidents.
We also put our son's potty in his room when he was training. It was there during nap- and bed-time. We stopped this when he got the great idea to pee into it while standing up. Needless to say his pee was everywhere except in the potty! =)
Because it is light out longer during the summer our six-year-old stays up longer. We allow him a bit of latitude and let him read in bed. He has a flash-light and a bookshelf full of books to keep him busy. This keeps him occupied in a quiet activity until his body and mind are ready to go to sleep. We started this when he was 4 years old.
His bedtime routine begins at 7pm, in bed by 7:30. Lights out by 8:30 and he is usually asleep by 9pm. I hope these suggestions help.
Good luck!