Had the same issue with a tomato clown that prefers a flower-pot coral to anything else, then his 2nd choice is frogspawn instead of an anemone!!!!
I was thinking almost about using a another tank....with only the clown and anemone inside to force them to be friends.... once they get close and casual then move em both back??? Seems like a lot of trouble but I think it might work, the completely bare tank with only a little sand will make the clown search for somewhere to hide.