S.C.
I would go the let him clean it route as well. I would also go as far as to have him wash out his underpants. He needs to see that he invests more time in cleaning up the mess than it would have taken to go to the bathroom. It doesn't have to be "punishment" it can be more like "uh oh, i see you had an accident here, you are going to have to help mommy clean this up." If you feel that this could be accidents and not intentional its a good way to go. Its not getting angry or punishing its simply cause and effect. When we make a mess we have to help clean it up, no biggie. However, if he takes the time to go in the corner sounds intentional. He is either trying to control the situation, or he is being lazy and not taking the time to go to the bathroom, or waiting until the last minute to go.