I imagine a slot in the battery would work, but I've yet to hear of anyone doing that to a working battery. Then again, I've yet to hear of anyone using a hacksaw to modify a center pin, so let me know how that works out for you.
Whether on the battery or the carto, the slot has to be there for the air to reach the automatic switch on a sealed battery. I believe the first sealed 808's had the slot on the battery rather than the cartomizer. I have heard of people who have slotted the center pin of a 901 atomizer to allow them to work on sealed automatics, so I know it will work. But since i don't own a dremel, I'm too lazy to put that much effort into it.