I have a 13month old who is currently breast fed at home, and I find that whenever I am holding him, he shoots his hand down my top! Noooooo!!! lol Not sure if him being breast fed has anything to do with that or not, but I always remove hin and place it down by his side when he does it.
I also have a 27 month old, who, since day one has always been a "leaner". He never stands with his two feet alone, always leaning on a table, a couch, a wall. Just a weird stance I suppose. Also he is ALWAYS slouching in his booster, he sits to the side, him bum half way down the seat. I am constantly telling his to 'sit straight'. A little annoying to look at and I always want to correct him, but probably just the way he is.
I don't know if I can help you, I bet there isn't much you could say to break this kid of his constant need for skin contact. Who knows, it could be more of a psychological issue for all we know.
Have you asked the parents about this, is he like this at home too?