What about a toadstool? Some toadstools will tolerate Clowns alright. I purchased a hairy toadstool for my clown (along with Xenia, Rhodactis Mushrooms, Clove Polyps, and Daisy Polyps). He likes the cleaner magnet.
My only concern about having Euphyllia and Clowns is that the fish can annoy them and cause damage to them. That said, I have two torch corals, three frogspawn, and a hammer coral in a 10 gallon display tank with the Clownfish . . . and he still likes the cleaner magnet.
Euphyllia aren't typically nuisance corals, though they can have a pretty fierce sting (especially the torch corals).