Retro fit dual zone? Everything is possible, but somethings are a lot more difficult than others.
Climate control has more temerature sensors, servos on the air flaps to mix and distribute the air around the car, as well as an automaticly controlled blower to maintain the set temperatures. To swap all this would certainly be a dash out job. Add at least 2 days labour onto the cost of all the different parts required and you would be looking at a fairly hefty bill. Plus the potential for future dashboard rattles.
In all honesty, it would probably be cheaper and less hastle to change the car.
