Well, I have been thinking on what would work, on and off, all afternoon and I came up with this.
I used some 4" pvc sewer pipe, 20" long, and two 4" pvc caps.
I cemented one cap on one end of the pipe and drilled and tapped two 1/2" pipe thread holes, side by side, on the other cap. Once the threading was done I teflon taped a pair of 1/2" x 1/4" bushings and threaded them into the cap. Then I teflon taped a pair of 1/4" x 3/8" hose barbs and installed one of them into one 1/2" bushing, and then plugged the other 1/2" bushing. I put the vacuum pump onto the hose barb and checked my work. It held vacuum for 15 minutes. I then removed the plug, installed the other hose barb and then cemented that cap on the pipe.
I hooked the assembly into the vaccum line on the truck (resting it on the inner fender) and tried it out.
When I first started the engine I found that there was no difference at idle with this plumbed into the system than without it, but when I rev'ed the engine to 2000rpm and pumped the pedal, it was soft as it was before. I let the rpm's drop back down to idle and tried the pedal again. It was softer than when I first started it up.
My guess is that this homemade reservoir is holding onto the 20" of vacuum produced when the engine is running above 2000rpm and is allowing it to be used when the engine is at idle.
I plan on painting this pipe black and mounting it to the inside of the drivers side frame rail. That is not too far from the power brakes and is out of sight.
Greg.