Resettable mechanical switch?
http://digikey.com/product-detail/en/A8GS-S1305/SW1533-ND/4248837 

Maybe try one of these. You could have a cap charged to 5V, a depletion-mode fet that is held off when your power is on and dumps the 5V charge through the coil when power is off? This would allow the switch to manually be reset even if power was lost and not purposefully reset.

edit: If it just needs to pop "ON" when the car turns on, have "ON" be the reset position. When the car turns on, have a circuit that momentarily 'resets' the switch to the "ON" position and then the switch will be toggleable.