Thanks Bryan and Alex.

I switch automatically, I have a pressure switch that activates the pump relay around 15is psi. Then a trigger wire off the pump's power that runs to a small hobbybox/circuit to drop to 5v for the evo 8 ecu and an LED on my steering column so I know everything is working. There is no float saftey or flow sensor... but maybe I will work on that down the road.

If I don't want to spray meth I can just disconnect the pressure switch and it will use the normal maps.

Setup something like this here for those interested:
http://evoecu.logic.net/images/4/45/ADC-evo8-harness.jpg