Get him to come up and feed off the surface first with live crickets. Then move onto freeze dried shrimp (soak them first if you have to). Once he is hitting those consistently off the surface, starve him for a couple days. Toss in a pellet and see what happens. Chances are he'll spit it out, but give him another pellet or two to try. If he doesn't take them, starve him another couple days before trying again.
I used this method on my 4" green sunfish, and it worked like charm. The trick getting them used to feeding off the surface. Live crickets worked wonders for me in the beginning, and then I'd smash them a bit so they weren't moving around as much.
