I got a Copperband solely for the purpose of eating aptasia hoping I could pass it along when my aptasia was gone so it wouldn't starve... It eats everything except aptasia... (Except for corals and inverts, it leaves them alone. Even my feather dusters). Not my .01 cent though, just a story
Most copper bands will eat it. (I'd say all, but after my expirience now it's most)
Also you could look into a matted filefish or berghia nudibranch. The nudibranch will for sure eat it, only problem is that they are small but the number of ways they could die in a tank is ridiculous. They have their own 1000 ways to die. If you have ornamental shrimp, they will eat the nudibranch. If the nudibranch falls into the center of the aptasia, it will die. Also they are pretty expensive... They have more plus sides than eating aptasia of course, they are rather easy to breed.
I don't know anything about the matted, haven't really looked into that one because I don't think it would have done well in my tank as far as aptasia food source goes and it'd be harder to catch and pass along than a butterflyfish
-Giancarlo