What do I do with them? When we switch everything over to the new tank, how do I get them off the heater?
If they are only in there.. I would leave em alone, messing with them can cause em to spread...
If your overflow can come out of the tank as one unit I would pull the whole thing out and drop em in a vat of diluted bleach(etc) and scrubb real well as it will allow you to get rid of them without them blowing their spores all over the tank... If you can not pull the whole overflow, and choose to get rid of the them, I would turn absolutely everything off int he overflow to trap the water in there without it getting to the rest of you aqaurium, pull em off and suck out the water that was in the overflow to also get rid of the baby aiptasia spores, then clean it real well.
When your ready to switch tanks I would just pull your heater and soak it in bleach(etc) and clean it off real well, or allow it to sit out and dry for a few days to assure no living bits survive on the heater, as the whole aiptasia can regrow from a simple piece of aiptasia.