I have run into this problem in the past and the solution I came up with is having the fan and light on the same circuit. You need to do the following:
1. run one three conductor from each fan/light back to one PNL-8[homeworks switching panel]
2. Have the homeworks person spec a HWI-4FSQ [fan controller] for fan and a RPM-4U for the lights
3. Both units need to be next to each other, I typically put them in locations 7 and 8 in the PNL-8
4. Feed them with ONE circuit and your problem with neutral seperation is solved.
5. Mark the units as on same circuit so future work won't overload the circuit.
The homeowner will have to accept the fans on the same power system as the lights.
