I've found there's good and bad trade offs w/ fifferent clowns, like the skunks may not be the best at feeding their nem, but they are the most passive IMO.
Clarki's seem to be great at taking care of nems, but can be aggro w/ other fish, same w/ the maroons.
I think the best chance for having more than one pair is pinks and occs.
My female maroon didn't feed her nem except for the stuff she didn't want herself, shrimp moltings, nori, both of which my nem doesn't really seem to care for either.
However, the new male is awesome at feeding nems mysis b4 eating for himself.
You may have the same luck if you add a male, but you know, no gaurantee.