peppermint shrimp aren't going to take down that colony! do you have a syringe? one that you can remove the steel tip from?
the best method i have found was using kalkwasser. kalkwasser can be purchased at the LFS
for a lot less than the aptasia cures at the LFS
all you do is mix it up into a thick paste, almost like toothpaste. suck it up in a syringe(without the steel tip) and squirt a generous glob on the mouth of each anemone. when they close up and shrivel down, squirt another glob on the shriveled leftovers. i would turn off all flow while you are doing this.
i would do about 10 anemones every few days, until they are gone. a large amount of kalkwasser in the tank can effect parameters.
redneck is correct, ripping them off of the rocks will exacerbate the problem.