try using candle wax (melt it into the depressions)then razor blade/sand it flush with the surface.
paint it,
then crack it out, it shoudn't stick too bad or anything, and you can use a wooden skewer or whatever to get the bits out of the corners (shouldn't damage the paint if you go easy)
i'd say there is a "proper" way to so this, but this method appears to be not too dodgy.
if all else fails, just paint it (the bare cam cover) with oil, like mine.