The system uses basically two elements:

1) the pedal
2) an electronic device (interface)

1. THE PEDAL

It's the point of my invention.
Quiete difficult to explain and maybe even more to build it.
Let's say that the pedal works like a kind of encoder (pick up) that "catches"  the pedal's turns and movements.
Each time the biker moves the pedal, the encoder sends a "message" to the electronic device "saying" that the pedal position changed, how much changed (distance) and in wich direction (forward or backward).
An integrated circuit inside the electronic device sends these information to the pc simulating mouse Y (vertical axes) code (actually the IC is like the one used for mouses).
If you try to bike while your windows desktop is on, you will see the mouse pointer going up or down.
We can say that the pedal acts like half mouse.

2. THE ELECTRONIC DEVICE

Nothing very much to say. Condensers, resistors, Ic, etcc...
Two switches (push buttons) are connected to this device emulating the right and left mouse bottons.
The electronic device is then connected to the pedal with a little cable that provides to bring low voltage at the encoder and to receive movement data from it.

You may ask me how do I shoot, fire or open doors.

Fire: pedals (mouse) backward
Open: pedals (mouse) forward
jump: push botton right (mouse right) double click
change wapons: push botton left (mouse left)double click

I know that other functions are missing but you can play also with your keyboard on the handle bar...

I tried VIRTUALBIKE with Doom, Duke3d and Quake, but I guess it should work also with every game that uses mouse as control device.