Brian, I hope you are not suggesting this as a simple way of building a compressor because not only are you wasting at least half the fuel, probably even more than that, that thing is dangerous as a cocked pistol! The only thing standing between you and a dangerously over pressurized tank is that pop-off valve which is designed ONLY to work occasionally, fortunately when they fail it usually sticks open but if it sticks shut you may be in for a world of hurt! As you can see from the parts 47 has listed it would not cost much at all to buy an unloader valve and throttle kick down and set that thing up right, the small cost for parts would be paid for almost immediately in fuel savings. You could get by with just an unloader but I would not recommend doing that, A POP-OFF VALVE IS NOT AN UNLOADER VALVE and should NEVER be used for one!
That pop-off valve is meant only for an emergency in case the unloader system fails or the switch on an electric outfit fails and should NEVER EVER be used for anything else, certainly not to regulate the tank pressure!