I see the idea behind it, but as previously mentioned, a mouse click, or indeed a key press cannot be applied progressively like a handbrake or pedal, its either on or off.
I have been thinking if about making some kind of handbrake type thing as well, but using a switch that is variable, maybe something like a volume control, which increases and decreases as it is turned up or down.
Now i don't know if it would actually work, but i was thinking if i find an old keyboard, take it to bits and re wire the connection on a key that i wouldnt use for anything, such as scroll lock, run some wiring to an old volume knob, join a piece of bar to it, and hopefully the handbrake would come on and off progressively as i pull the bar up and down.