If your Z3 is drive by wire like the E46, and it's anything like the E46, I think you can just use your auto pedal. I've taken apart both a manual, and automatic E46/E46 M3 pedal and they appear identical save for the "kick down" clicker in the auto. You can open up the housing on the pedal and slide the clicker out.
If I remember right I think there were two types of DBW pedals, one with a potentiometer in the housing like the E46, and I think the other had a different set up. Either way I think functionally they may be the same but I would double check. I am assuming your pedal is the set up the E46 had with everything inside the unit.