Since you can't block them have you though of putting in some liquid forms of food also until moved to the bigger tanks? I've been target feeding all my stuff with liquid zooplex, phyotplex and chromaplex (on a rotating basis) every couple of days. I know this can't be the main diet for your corals but it might keep them healthy until you can move them and the thiefs can't still this stuff away.

When I feed my clowns I also give them some food from that but my peppermint shrimp is quick like you said. I think he gets most of it so I depend on the other stuff so they don't starve. Everything is growing (almost too quickly).

People may have bad things to say about this stuff though. I also don't know if you would have to increase your water changes because you don't have a skimmer right now. I like Greg's advice this was just in addition.

Angie