[petek]

Something that might work pretty well for you is to create a circuit with a couple of relays along with a push button and connection to the normal brake light circuit.

Push the push button and the brake pedal at the same time and the line lock would come on and stay on. Touch the brake again and the line lock would drop out.

No toggle switch to leave in the wrong position and a bit of fail-safe (touch the brake pedal and the lock drops out).