I'd think you'd almost need a stunted bass population to have a chance at containing the crappie. I've seen several small ponds with stunted bass populations offer up large panfish. The main problem then would be future generations of panfish at low numbers. It would be advantageous to have ample amounts of shoreline cover if you went that route to give the younger fish a chance. Your other option could be to buy a fairly large amount of fathead minnows per year, feed the bluegill and throw out virtually all crappie under 8 or 10 inches. You'll never catch enough crappie to entirely wipe them out of the pond. I'd imagine that it'd be hard to maintain a pond for crappie and bluegill for a period longer than several years without atleast some bass or extensive amounts of fishing and tossing fish though. This is just my two cents if you're determined to go with just those to species. Good luck.
