In theory, I guess you could set it so you the Gauls can only "jihad" on gallic regions no longer owned by gauls, representing the gauls unification when they were threatened with elimination. Not that I think that this is what it should be used as, but I think it would work in theory. In MTW2 I think you could only Jihad on muslim regions not owned by a muslim faction. Then again, that meant you could Jihad the rebels, so that would be kinda tricky, don´t know if you can get around that.