I generally agree with those that say that "once nipper, always a nipper"... since once an animal finds a food source that apparently satisfies their nutritional needs in a way, they will continue to view it as a food source in the future. The only way I can see one probably getting a "nipper" to stop, is to either: 1) Satisfy their nutritional needs going forward or 2) Remove it from the environment, get it eating all prepared foods that would satisfy its nutritional needs, and the place it back into the old environment... even this would probably be hit and miss and depend on how long you removed it and whether it ends up accepting the new foods going forward.
Having said that, I also think that a majority of the angelfish that Copps has in his tank were quarantined and acclimated to prepared foods (including a variety of frozen angel food and vegetable matter) before being placed in his system... making sure they were getting a varied diet BEFORE they even entered the system. This, I would assume, guards against the angel looking at the corals to satisfy their nutritional requirements while being acclimated to accepting foods that actually do satisfy their nutritional requirements.
It's not always how much you feed them, but WHAT you feed them that is important. The one thing I didn't see on your list of foodstuffs was some type of algae/vegetable matter (which may be in there, but you just didn't mention it). Since you have a dwarf angel (which is primarily found in areas with algae growth and is a large part of their diet), this could be a part of your problem.
Hope this helps... good luck!
Chad