7-yr-old & daytime wetting

[gbd3]

I have a 7-year-old son who has been wetting his pants for years.  I did take him to a urologist and a psychologist related to that office at the Children's Hospital of Philadelphia.  We've had lots of tests including x-rays, ultrasounds, rectal examinations, and tests for all kinds of infections.  All have come back normal.  We've used incentive charts, watches with beepers, etc., all to no avail.  He does take ditropan, which does help him, but he's certainly not cured.  

We recently started taking TV away for a week at a time each time he wets his pants because he can't seem to watch TV, play video games, etc., without wetting his pants.  For the first time, we've had multiple instances of 15-straight-days of daytime dryness!  Unfortunately, as soon as that TV goes back on, he's wet again.  The same thing applies for playing outside.  He's at a day camp for two weeks right now and has come back wet each day.  

I'm at the end of my rope here.  He's obviously physically capable of getting to the bathroom and staying dry when he really wants to....so what do I do for him when he's at camp?  I'm afraid he'll be tortured...some of his friends from school are there and I'm afraid they may begin distancing themselves from him.  We already held him back a year in school to try to let him catch up from a maturity level.  

In every other way, he is the sweetest child and fairly obedient.  I'm filled with self-doubt about this whole punishment route I'm taking, but so far it's given us (and him) the best success yet.

Has anyone out there had a child like this who just grew out of it on his own?  Am I making this worse by adding punishments?  When we tell him that he needs to stay dry always, not just for one day, he looks at us like we have 10 heads....I swear, he just doesn't get it.  Any help would be appreciated.  This has me in tears.