Choo choo, I had the same anenome growing out of my new live rock too. And like you, I was excited that it was growing, until I found out that it was aiptasia. I bought a peppermint shrimp. 2 days later, I was in my LFS and I thought I'd get another one. The second peppermint shrimp ate the aiptasia within 30 minutes of putting him in the tank! I guess he really likes that stuff.
I'd try the shrimp route. They are neat to have in there anyway.
Good luck
737Mech