After reading this thread I had a bit of inspiration that could help FiXeR_nl with his request. A few years ago I purchased a joystick with auto fire. On the back of this joystick was a dial to set the speed of the auto fire. I have today dug out this joystick and plugged it in. I have tried to see the auto fire at the throttle and tune it to hold an accurate speed. It does work to some extent, the acceleration either climbs very slowly or drops very slowly. It will not hold a consistant speed, however I think its the closest your going to find to what you want. The only advice I can offer is.... go and have a good look around the joysticks and joypads avalible and see if any of them have a simalar system where you can set the autofire speed.
Another bit of advice, get that wall brick you have been talking about and chew on it for a while.