Wow!
It sounds like you're doing everything right (cutting off fluids after dinner and making sure he goes potty right before bed...). You must be so frustrated.
My boyfriend's 7 year old son still periodically wets the bed. We spoke to his doctor and it was discovered that due to enlarged tonsils (or whatever the reason), he sleeps so soundly that the normal urge to urinate doesn't wake him.
Does your son snore?
Also, I know there are some easily treated overactive bladder problems that some kids experience that you might want to look into.
Since you've already done all the obvious stuff to correct the problem, I would try setting up an alarm clock in his room and teaching him how to use it. Set the alarm to go off in the middle of the night and then again early morning.
He should be able to go to the bathroom and then right back to sleep I would think.
No matter what you do, I would absolutely NOT go back to Pull Ups or diapers.
I hope this helped and good luck to you!