I'm grasping your situation and putting them both on one might work ok but since its already split with two systems you might as well take advantage and do it the right way by moving one of the thernostats further away. That'll also provide the best comfort level. Some people spend a lot of money to get that sort of control. It wouldnt even be too hard you could replace one of them with a thermostat that uses a wireless temperature sensor like someone else mentioned.