Hi! wow! Your experience sounds just like mine with my 10 year old, exactly the same about the pooping and the DS, PS, etc. He'll get punished for 1 week without any video games., etc.
Did you figure out what was wrong with your boy? I think I am gonna try the Mirolax, and see what happens.
Has your son seen a pediatric gastroenterologist? If not he should. I don't feel he is doing this on purpose and I would not punish him. Until he has been thoroughly examined by a GI doctor. There are a couple of things that can cause this, so I would have him evaluated, and go from there. As exasperating as it is for you, it is also for him, and obviously causes him a lot of work.
My seven yr old was doing this for awhile. He was also having behavior issues at the time. However, I took him to a psychologist who specializes in encopresis. She had me make a chart with the number of times he tried to sit and poop and the number of successful poops he made in a day. There were seven rows for each day of the week and I just put an x in the box if he sat. Then we did a poop journal for a few weeks with the description of the poops. soft, hard , little, big, med, and the dates and times. Okay that helped to develop a pattern. We also started mirolax. Like a half a lid ful in his drink every few days in the beginning. (at first it was messy)Then we went to once a week and then every other week etc. till we got to a good place. It ended up he was constipated. I didn't know this but the poop was leaking around the backed up poop. They lose the feeling to need to go because the muscles get weak. It comes out in the pants. We were finding poop everywhere. The registers, carpet, walls, hamper, toilet seats, underwear etc. It was so bad. He was actually picking it to help it come out. Then he would get it on his hands and then it would get elsewhere. I was so upset and always disciplining him but really I discovered he couldn't help it. When I notice it getting in his pants or see it in the shower I know to get out the mirolax again. I hope this helps.