I agree... with kurt_nelson. I have a pair of true percs and I got an anemone for them that was supposed to be one that they would go for. They are totally not interested. However they have a nook in the live rock where they are doing the same thing your clown is doing.
As far as frogspawn goes, I have seen one used as a surrogate anemone at my lfs
and those clowns are all over it. From what little I know about this hobby, I know that clowns are unpredictable and you may or may not get them to host an anemone. It's hit or miss.