Wow, looks like it's getting good shade...
Hmm... I assume the clam is strongly attached to the rock. Maybe the clam will 'jump' to a new location...
If it's annoying you a lot, you can always try and move the anemone. I have much success 'tickling' pink tip anemones. As for the larger ones, I don't remember what I do to them, but try 'tickling' the base for a few minutes and see what happens. It should cause the anemone to shrink and maybe let go of the rock.
Good luck,
James