That reminds me of the brake lock system I had on two different old tow trucks.!! One was mechanical,and one was electric-but just as you say,you'd step on the brake and flick the switch[or lever on the mechanical one] and the brakes were locked down good till you released it!I don't know if any of you guys have ever been around forklifts, but, on some I've seen they have a valve in the steel brake line. You apply the foot brake, and shut the valve. I think drag racer's use a similar type valve, a line lock, I believe thats what they call it.