With N/A you can set the pump to be too rich at wide open throttle, and just keep your foot out of it until you want that fuel for NOS...
Its all about foot control... If I crank up the pump 10%, i will have to travel less distance to get the same fuel level as I had before turning it up, but i can mash the pedal down fully to have more fuel (after turning it up). Pretty easy, unless you are one of those "all or nothing" drivers