Anemone fish can adopt almost anything for a host, the ultimate concern, though, is going to be whether the relationship is good for the fish and the host. As far as getting the perc to vacate the brain, I would also suggest moving the brain, maybe the clown will stay in his already established territory instead of following the brain. Obviously, it would be better to give it a new host, but try moving the brain before you do that if you're concerned about a delicate anemone.