Maybe instead using dice, which has been brought up before, and I don't think the use of them will ever be mandated by a specially ability, it could be "Once per turn, if more than one hero is opposed in battle, you may withdraw a random hero from battle."
That way it isn't too splashable for auto blocks. Maybe you could even add something like "If you have a Pharisee is play, you may discard this card and Judas Iscariot to withdraw all heroes in battle."
That could also give it some more historical background without completely making it useless without the required ECs. I realize it's quite different from what you were aiming for, but I just thought it would be cool.