Are you looking specifically for DUELS? In otherwords, you want to use it in a duel and NOT [siege war, or random pk, or in arena]? Duels only? If you want to use it in pvp in general (when fighting players anytime, sw dueling arena etc.) then you can check whether your target is a player or not via
UnitIsPlayer("target")
which returns true/false, and can be used in diyce use = X Y Z portions
Also, out of respect for the makers of the addon, try to spell it correctly. it is D I Y C E . DYICE is like "die young in crappy environments".