Why do you buy live clams just to go and freeze them? Just for the freshness?I don't find them finicky at all. First of all, don't quarantine it, they hate that.
In the sea they eat worms that they use their long snouts to get. I feed mine clams. I buy live clams and freeze them, then shave off thin pieces. My present copperband is about 10 years old.
I also give him live white worms or blackworms. A good commercial food is LRS Reef Frenzy which I use as my staple.