what's wrong with just spec'ing a low voltage box at each thermostat location...run a length of conduit for those that will have access issues...heck do conduit on all of them regardless...how many are you talking about?
Well the conduit has issues because of obstructions in the walls. I can probably do with as few as two temp sensors, one upstairs and one downstairs. Maybe I'll run 7 wire thermostat cable and cat 5 to each spot where I want a thermostat or temp sensor.