I would want them on 2 different switches.
Like Knox said, leave the fan switch on the dash but add a switch under the seat for just the pump. This way you have ambient air without the pump and heat with the pump.

However, make sure the pump coolant line are aux hose loops and not part of the main
trunk system. Otherwise, you are going to add restriction to the cooling loop by not spinning the heater pump and could overheat the engine.