Live mussels worked for all my butterflies. Just scoop up a few fist fulls of 1/2" mussels from under the piers and keep them live in the tank. That way as the butterflies pick and eat them, there isn't a massive pollution bloom from a regular sized supermarket mussel dying off. Tiny mussels are also very soft versus tough and chewy clams.
I'm able to get most of the wild caught butterflies I catch here to adapt to aquarium life simply on mussels. After that theres a bit of training to dry food, but then my success rate drops, but I think if given enough time they would all adapt.
I don't bother with copper banded though, since of the 4 that I ever tried, only 1 of them was even trying to eat, so at best, that would be a 25% rate of success, but I didn't know about mussels at that time. Just a little bit too frustrating for me to not be able to know what condition they were in before they arrive at the shop.
Oh and as for loving my butterflies, since I raised them from tiny 1/2" size to the giant 3+" they are today, the only coral I have left are zoos and ricordieas. I guess one day, I may just swap out all my fish for stony corals again.