Cowfish all have personalities like puffers so really i would test it out with a feeder shrimp such as a ghost shrimp however they are known invertebrate eaters.
your best bet is Palaemontes Vulgaris because unlike ghost shrimp they are a saltwater shrimp and will survive longer in the tank and will clean if not eaten right away so you get 2 for 1. You can find them at;