Would it be possible to change skin-toned heads into Yellow ones? A sticker won't work, because the whole head is of whatever that colour is. But could you actually paint it?
Another idea would be to use that silvery stuff TTK used on the armour. You could make a large stock of round silver.. thingymajigs.

(This is, of course, for peopel that don't wnat these figures. Personally, I think it's a shame to waste LEGO, so I'm just trying to figure out a good use for these things.)