Add a normally closed switch to the end of the P relay. Solder the extended slate+white wire to one lug. Solder the new wire that you added from the J relay to the other lug. Which wire you solder to which lug is immaterial. Here I used a white wire with an orange tracer.

The switch that is added should be arranged as such: spacer, long blade, spacer, spacer, short blade, spacer, switch stack backing plate, screws. Using the right length screws is important as they cannot impinge on the relay armature.