If you want to strongly encourage, you could put the two of them together in a bucket/qt so the clowns can find the nem without a big tank/ other corals, that way when they both go in the display tank the clowns will see the anenome and recognize it as a safe spot instead of hosting elsewhere like a return.
That being said, I have clowns that host in mushroom corals, and clowns that host on the return pipes, so what do I know lol...