I was just talking w Mike @ Musclerodz about this yesterday. Like you my big hold up was routing the cut-off switch through the rear of the car.
Glad you're thinking safety Todd...
Maybe in 2017 I'll get to it
EDIT: Another thought I had is maybe a cut-off lanyard like boat racers use? If they get thrown from the boat it kills all major systems so you don't get mowed down.