With seastars there really isn't a secret. It seems to me there are two different categories, those that we do know what they eat, and those that we don't know what they eat. Most of the "we know what it eats" are generally considered reef unsafe. Having said that I had 2 CC stars for many years and they never touched polyps, preferring to eat the nori I rolled over PVC pipe that I offered them. Maybe they would have gone after clams though had I had any of those in that tank.
Any of the ones we do consider safe are of the "we have no idea what they eat". Fromia, Linckia and their relatives for example. Unfortunately they either adapt to captive life, or they don't. IMHO there's really nothing a person can do to influence the outcome other than giving it a try and seeing how they do. Either they'll live a couple years or they'll die within a couple weeks to a couple months. Or so it seems anyhow. For the most part I've given up trying these kinds of seastars myself but as with everything YMMV.
