DISCAIMER - i have no idea bout pathfinder setup, im talking general knowledge.
Similar to what Kami said, but u dont need to run a new wire.
can u access the wires connecting to the knob inside the car?
if yes, strip the wires without cutting them (there should be 4 - HI / LO / Fog / Ground)
get a multimeter and do a continuity test to see which cable is the one connecting to the fog lights. the way to do this is to get a long wire, and disconnect the fog light plug. stick the loose wire u have into the socket and bring the other end inside the car with you.
test this cable with the other cables u stripped to see which one beeps on the multimeter.
disconnect this wire from the Nissan light switch, and connect to ur new switch.