Too bad it wasn't wintertime still. My DS1 did this, and I had to cut the feet off his blanket sleepers and other sleepers, and put them on BACKWARDS!! haha! He couldn't get to them to unzip them, and he used to get so mad!
He is taking the onesies off too? Dang!
Maybe you can try and potty train.. it wouldn't hurt I guess..
I know how you feel about him playing with it.. I walked into DS1's room and there was poop everywhere! All over the floor, walls, toys, heater vent and HIM! He looked like one of them mud people from King Kong movie! LOL
Hope he stops doing it soon! My son only did a couple times..