Cool rig. You can run them off a hose, I have in the past... used a T designed for I think radiator hose, picked up from O'Reilly's, that you can screw a garden hose onto the side, and then have to block off with ball valve like you say, or at least partly to allow most water to flow to engine (you don't want pump/impellor to run dry, put another hose in it if need be, can do from the back of pump... just like the Berkeley videos they have on their web site). FYI... One thing to consider, however, I had my Berkeley pump rebuilt this spring from Hi Tech Performance, Shell Knob MO...
http://www.hi-techperformance.com/ great sorce of info for all pump stuff BTW. Duane Oblander gave me strict instructions (and warranty stipulations) not to run it unless in lake... to name a few, the impellor is hydraulically balanced, running dry basically grinds any road debris up on wear ring, ect., etc., basically meaning depleted pressure and performance (the upper 5% type of thing). I understand that's not very practical at times and the need to run in the driveway... these guys race jet boats and want to preserve the most performance you can squeeze out of them, so basically I try not to now unless I absolutely have to.
Mark
