I think the main reason for the spells to do not be included in the hall of enable backstab actions is that you should be able to speak, wich breaks the surprise of the atack. Also, ranged atack are not enabled as this simply because it'd be cheesy to backstab someone from the other side of the room with an arrow.
And backstab would be a tool of the Gibbering twelve if it could be used with magic. Have you guys ever imagined a fireball with a damage multiplier?
