Seat Heaters

I suppose if you were comfortable with modifying electronic/electrical circuits you could do it. In my old honda fit i installed heated seat pads on the front seats i bought off ebay, then covered them with leather seat covers. As i recall the portion that is attached to the seat is simply a element with wires hooked up to it, not much different in function to your electric stove element. control of the heat was from the switch so in theory perhaps just changing out the switch to a newer one with 2 settings would work..
That said, i am not one who is comfortable with doing such a mod to my seat heater wiring and risk melting my softex seats or starting a fire..