You basically don't...they will make that decision on their own
If the flow was terribly high where your GBTA is..it would probably move away on it's own.
We had folks here with clowns that have hosted just about every odd thing you can imagine including powerheads and overflow boxes..just give them some time and they should settle in and find something in there they want to host, nothing you can do but wait :tub:
You could put a picture up on the tank to try to "teach" the clown the behavior.