If you open the blower door there is a kill switch there, that will activate, this only kills power to the point past the blower switch which is every component in the furnace, I need to ask what you need to kill the power for to tell you if this will suffice for you.
Removing the blower door should do it, naturally I would ask that confirm that with a meter but if you can't you can't, either way if you are careful with the wire on the stat that is connected to the C terminal or an X terminal you won't cause any damage to the low voltage transformer.
As long as you don't touch the wires together, the only concern is burning up the control transformer.
Remove the blower door and that should kill it though.
You can wing it,
The terminals will be exposed when you remove the front of the thermostat, its where the wires are connected at, they are lettered.