Limit video time and TV time to specific intervals of time- say 30 minutes at a time. With the rule that he goes to the bathroom before and after the 30 minute interval. Leave these instructions for any other adult who is watching him.
Set a timer that will regularly go off in 30 minute intervals. Of put a lamp on a timer - so it will blink in 30 minute intervals - something that will catch his attention. Heck, put the TV and the computer on a timer, so they shut off in intervals.
When playing with friends - get him a watch that has a alarm - set it - when it goes off, he excuses himself and runs to the bathroom.
With cues - he must get up and got to the bathroom.
If you think it is a matter of his ignoring his body's signals, then you need to "train" him to listen to them. And a little discipline on this one really will not hurt him.