[Jeremiah H]

Something we came up with, as an alternative (if we don't need the compressor onboard or just want to do something different) involved a piston, screw drive assembly, and a little motor.
The idea is that you rig up the end of the piston's rod to the nut of an acme thread (or KoP, whichever) screw drive and mount a small, fast motor to the screw. The piston is staged with the rod all the way in, with the nut at the extreme nearest point to the piston. Your vacuum line is connected to the piston at the opposite end from where the rod enters. The other end (nearest the rod) is left open to allow displaced air to escape.
When you want to produce a vacuum, all you need do is power that motor until it has driven/pulled the rod far enough to create the desired vacuum strength. You could reverse this idea and start with the piston all the way open and the vacuum line connected at the other fitting, then push the rod in until you have the desired strength. You also could push/pull the rod with a cable or lever or something else.
I think this is allowed, but I must admit that I haven't gotten too far in this year's manual yet.