you could do it yourself, you can run it off a powersteer pump, and run a hydraulic slave cylinder, then you just need to program a pic to control the valve that controls the flow to the valve, the higher the rpm , the faster the valve operation, so for slow takeoffs, you rest your foot on gthe pedal and it engages slowly, step on it and it drops it etc...
easy to do if you can do all the things yourself, but very costly if you cant. I met a guy at home that did it himself and it works very well.
cost under 1k