I think you could use a thermo switch and use the stock temp sensor as a reference to activate the switch. I havnt tried it yet, but thought about this last night. Im hooking up electric fans into my SC today. Im a bit lazy and I usually just use a basic ignition tap + relay and let them spin until I pull the key out.
Check out your local Radio Shack as they will most likely sell a kit you can assemble yourself that will allow you to turn fans on and off at whatever temps you want.
I use one and it's been 100% reliable.
Whilst we don't have Radio Shack in Australia I use a kit from Jaycar and no doubt the kit is also available in the States.
I have a fanswitch that I fit to the radiator or to a fitting in the top hose. Turns on Around 92 and off at about 88. Of coarse wired with a relay. Works well and is easy to fit. Cheers
go here and u will see digital fan controller 2nd pic down
they are fully adjustable from 70 to 100 degrees
and can adjust turn on temp in afew seconds whenever u want
also tell su exact engine temp too