There is a company in Japan called Roberuta that makes a system that fits to the topside of coilovers for high end exotics. I believe it is a pneumatic system. It is now also being marketed for coil over kits for other types of cars. It isnt anywhere near cheap. But its exactly what you are talking about.
From their info:
"Imagine being able to raise or lower your vehicle's ride height at the touch of a button. Steep driveways, flatbed tow trucks, and jacking up your vehicle with a standard jack all become effortless. Lowering your vehicle to the absolute maximum for your next car show is possible without readjusting your coilover at the show. Life becomes simpler and you can spend more time enjoying your vehicle."
website is roberuta dot com
Dig on that-
eric