Drive by wire certainly wouldn't be difficult. It would just need some investigation of the voltage range produced when pushing the accelerator. This made even easier as this data is available via the EOBD socket and a laptop. One slight fly in the ointment is that there 2 sensors in the pedal mech. The outputs are compared by the ECU and if the vary too much the car throws an error code and goes into limp home mode for safety. It would only be a case of ensuring both sides get the modified signal however. By far the hardest part of your project will be reading the current gear.... Perhaps it would be possible to just use a generic blip for all shifts?