Something that popped into my head while reading this was that Crappies are primarily filter feeders until they reach around 6" in length. Could be worth a shot? Of course, once they reach 6", they become primarily piscivorous and might compete with Bass for food, but their offspring would also become food for the Bass, so maybe it'd even out.
I know, I know, there's no such as a balanced pond. It's always leaning in one direction or the other.
