The pvp rogue profile Sheruon has already does this pretty much, you do have to have them targeted but it auto saps.
Code:if UnitCanAttack("player","target") and not UnitAffectingCombat("target") and not UnitDebuffID("target",6770) and UnitCreatureType("target") == "Humanoid" and CheckInteractDistance("target",2) then return true end