I think theres a second relay/control box that controls the headlamp washers. The only fire up with the lights on, and i think every third spray or something.
I guess you could just piggyback the existing headlamp washer feed though and have both pumps fire up together? Would mean you'll use more washer fluid, but would be much simpler.
I can find the wiring diagrams for the stock setup for you if you want?