I agree that it really is hit or miss. When i first got my BTA, my O. clowns wouldn't go near it.
So i did some research and read this post about a guy putting one of those lettuce clips that look like a clown fish next to the BTA. He said that the clowns think it's another one of them and they'll go check it out thus bringing them closer to the BTA...which he claims helps them begin to host in the anemone. Now, there is no real evidence that this method works but I tried it and my clowns were hosting within a day. It may have been luck but I would at least try it. My $.02.