I wouldn't bother with boiling the rock as you'll kill everything and will have to re-cycle the rock before you put it in your tank.
I would manually remove as much of the HA as possible, then put it in a dark container (as sphelps suggested) with a powerhead and heater and I'd add a handful of hermit crabs and close the lid on it for a few weeks. Hermits actually do their job when they're hungry (ie nothing else to eat) and they might actually speed up the process
