You could do this, you just have to use a timer to check if the contacts display picture is different every 5 seconds or so, then if it is, set your display pic to there's. In fact, if you set a messenger DP it already has it does nothing so you could just tell it to set the DP to a contacts every 5 seconds.
EDIT: Beat you! *Points down*
Great minds think alike, idiots seldom differ.