I'm wanting to get the bedrooms zoned. There is access to the supply for that area where it splits off the main run. Problem is there is no attic and this is on second floor so no access from below either to run zone thermostat wiring. I had HVAC guy come out and he said that the wire for the thermostat can be fished through the supply duct and then out of the duct into the wall in the master bedroom where the thermostat will be located. Is this possible or is this a big no no? Thanks for any help you can give on this.