QT all corals and inverts for 76 days. That's the only way to guarantee that these diseases won't get into the system. Dips won't kill the tomont stage of these parasites as not even copper will do that.
I'll say that if you go this route of treating your fish with hydrogen peroxide instead of copper, you should take the copper out right now. to have a good experiment they shouldn't have been exposed to copper first - this will skew your data. IMO if they fish are doing fine in the copper, then go ahead and save their lives that way. Find a fish with velvet at the LFS and try your experiment on that one. This way you can start-to-finish treat him with the H2O2 and get real results, whatever they end up being.