You don't need to use the Detail Spray in excess when drying. I found that one long spray over a wide area (like both doors on one side) works well. You only are looking to lightly mist the surface (it also helps to blast off the majority of the water with a leaf blower or compressor if you have one, you'll have to use even less Detail Spray afterwards).
Remember, this is after washing, therefore the amount of dirt on the car will be minimal, so there isn't a need to use as much DS as when you are using it with an MF towel to wipe off dust. Drying my mom's Ford Five Hundred, which is a considerably large vehicle, my bottle of Detail Spray went down maybe a tad more than 1/2"