There's something out there called a SuperMID, but I can't find much info about it or where to buy one.

If you're handy with a soldering iron, this looks promising and kinda cool:
MPGuino - EcoModder

Alternately, I've not tried this (but the logic is certainly sound), a simple vacuum gauge can help you visually see how much load you're putting on the engine.
Sunpro 2" MECHANICAL VACUUM REPLACEMENT GAUGE : JC Whitney: Auto Parts & Accessories