Furnace operated ceiling fan
There's a handy device which incorporates a temperature sensor and two output drivers - the LM56. I've used these as fan controllers for wall-mounted radiators - a fan on top of the radiator comes on when the radiator heats up, and so spreads the heat away from the wall. You could use the same idea with a suitable interface to your ceiling fan. The only thing to watch is the maximum ratings of the LM56 - 12V supply and 5mA output drive.