I would try frozen cyclopeeze, or some kind of flake - if you havn't tried that.
My lfs recently gave me a Citron clown in hopes that I could get him to eat, because he was being pushed around at the store and wasn't getting any food. He was possibly the most pathetic creature I have seen in a fish store. When I got him home, he wouldn't eat mysis, plankton, pellets, finely chopped krill, or a reef blend. He would however dart at some garlic covered formula two flakes, and frozen cyclopeeze. He started to gain some weight and look like a real fish, but he had a bad habit of sitting on my brain, which eventually had him for a snack.
Good luck