[DaveK]

Adding another clown is always an "it might work" kind of thing. As you point out, maroon clowns are very aggressive. Also, you clarkii might feel that both anemones belong to him.

My first choice would be not to add an additional clown. My second, if I had to have another clown, would be to try an additional clarkii. That way you might end up with a pair. I'd also be willing to return the fish if it didn't work out..