The tow package ones had to be filled with air manually through a schrader valve from memory. They are a Monroe product, possibly max-air? The factory FX3 auto levelling system is more complex than it sounds because it runs through the interior light sytem to avoid lowering while you are in the process of getting in and out of the car. They aren't that great to be honest, I've had 3 or 4 replaced on my Grange just from the rubber splitting, not even towing.
You could buy a statesman compressor, shocks and lines, skip using the sensor and use a switch to bridge the terminals that "trick" it into raising and lowering (using the methods described in the workshop manual for diagnosing a faulty compressor) but you need to be fairly confident in your abilities to wire that up.
But reading through sounds like you want a desired result without paying so not sure how to give advice on that subject..