Try crickets, especially if you don't mind hand-feeding them. Mine come running over to my hands to check for crickets!
They also love strawberries and other soft, sweet fruits, crushed into mouth-sized morsels.
Good luck. I hope you can get a companion for him. They do get depressed when they're alone, and that will cause them to eat less.

Good luck. I hope you can get a companion for him. They do get depressed when they're alone, and that will cause them to eat less.