i had to put ALL of my corals and 300lbs. of LR in buckets and rubbermaids to get a clown tang out of my reef. you could try a fish trap, but it may or may not work.
i think your only SURE FIRE way is to remove EVERYTHING from the tank, catch him, and put it all back ... in the same night (or day). i considered it a good time to reaquascape my tank. it took 5 hours to get it right, but now it looks better than it did before.