http://www.aqualandpetsplus.com/Oddb...0Stonefish.htm
-Some general info there.
I would suggest frozen silversides, market prawns (any shrimp really), tilapia, whitefish, squid, bloodworms, earthworms/leaf worms, ghost shrimp gut-loaded, freeze-dried and frozen krill, crayfish, etc. If it's still stuck on feeders, instill a starving period.
78F
1.005-1.009
IMHO, these fish would be better suited for a species-only tank.
Though, you could essentially try archers. More so of a top dwelling fish, that gets fairly large enough. Not a huge competition with feeding, and non-bothersome of the stonefish.