Boiling water trick....... the catch is "it MAY work"...
I would do 2 things. If there's not much you need to salvage on the rock, take the LR out and scrub it clean. Simmer the rock into kalk solution if you have to.
2. If there are corals you want to salvage on the rock, siphon the aiptasia out instead. Use a rigid air tubing attached to a python hose connected to faucet (You will have to do some modification on the hose on your own), turn on the faucet to create a strong siphon, suck the little suckers down the drain.
I would personally prefer the first method.