I think that might require the person in question to stand still and give him time to work; he's only done it against a human once I believe, against a stationary target.
Well, he's used the within thing in two circumstances, really. Once, against a lone gun thug who was standing partially in darkness anyway.
Two, against living statues of a nemesis of his. Notably, he couldn't do it while they were bathed in really strong light (I think to use the darkness within someone or something, he needs at least a little outside darkness to connect), but in more normal conditions he was able to remove stone limbs and such no prob, even once destroying one inert one in public with civilian spectators not even realizing why the statue just crumbled.