If you redesigned the cockpit, make the accelerator and brake controls hand operated leaving your feet to do the pedalling. You'll need to think about the steering interface as a normal steering wheel setup does not leave much room for the motion of pedalling with ones legs. Seat design would be critical as well. Perhaps you'd want to adopt a recument type position in the driver's seat. My guess is that after you've thought out all of the major issues and designed the vehicle to be as light as possible such that your pedal power yields a reasonable power to weight ratio, you'll end up with a bicycle with a small gas engine on it.