Do a trial measure for length and get a similar length cable set-up from a wrecker. Either feed it through the hole in the firewall and tie it to your big toe or take it across to the drivers window and use it as a 'hand-throttle' so you can drive it to you local cable maker and have the cable cut and shut to fit.
This assumes that you have modded the top of your existing pedal to take a cable assembly. Best way to see how this is done is to grab the pedal from the car that you are stealing the cable from. Maybe with a ounce of luck this new pedal could be modded to fit your car.
Cheers,
Mitch.