I have several idea's in my head that might be done but I'm not sure that if descides to implement something like this... Thaty they'll actualy use our idea since it might unbalance the game.
Therefor I suggest using a specific LB in the form of a skill that is equal to all classes. An LB skill that you can activate from the start of the duty and that cannot be activated again in the same dungeon once used (doesn't need to build up).
An enhancement LB wich adds to the strength of all your skills/spells (including the effects and the shared LB if its still unused) for lets say 15 seconds.

There are a few other possibilities but I think this would be one of the easiest to implement.