MSD 6A battery kill switch wiring

This is probably one of those situations where I go "DUH!!" when I figure it out, but here's the question:

Wanting to be NHRA legal, I have a 1/0 battery cable from the rear battery through a kill switch to the starter, then to the big post on the starter relay. I have the alternator charge wire to an aftermarket control/fuse panel under the dash, then to the hot post of the starter solenoid. (The field wires to the voltage regulator.) Ignition is fired by an MSD 6A box. MSD says I can ground either the white or violet wire (whichever is NOT used to power the distributor) to kill the ignition.

I have a 4-pole heavy duty QuickCar battery kill switch next to the rear battery battery. I can kill the battery positive, of course, and I'd like to use the small poles to ground the ignition... but how do I do this?? The small switch poles are closed (connected) when the battery is in the system, but open when the battery is disconnected. Opposite of what I want. So is there a simple way to ground the MSD box with this switch? I can't run to ground through the switch or the ignition is grounded when the battery connected. Am I missing something obvious?

I know there are other ways, but don't to complicate things. If I can ground the ignition and ALL battery power to the front is disconnected, I'd be good.