I had a problem with one of the boys peeing in the corner although I never did work out which one of them was the culprit!
I cleaned the carpet thoroughly and then pulled it up and replaced the underlay in the area immediately beneath it and also scrubbed the floorboards.
I banned them from that room until the area was completely dry and then positioned a plant in the corner to keep them away, I think the trick is to get rid of the smell completely (otherwise it seems to attract them back like a magnet) and also to break the habit.
Could you keep him out of this room completely for a few days? of course there's always the possibility that he will find another corner he likes just as much, so some strategically placed objects in available corners may help.
Another thought - does he have a cat bed? if you put his bed in the corner he may think twice about toileting there? if it's a territory thing and what he's doing is spreading his scent, then as the bed will already smell of him he may consider it's no longer necessary to pee there?
What is it about cats and corners anyway