If you do manage to find them, creep into their room late at night, perhaps with a balaclava. Then make certain that they sleep naked. Turn the heating up so they pull the covers down. Then, rid yourself of the natural barrier of going near their arse and slip a chocolate button or two in their arse crack.

When they wake up, it would have melted and they will think that they have followed through in their sleep and they might feel slightly ashamed or something.