Hate to break it to you guys, but unless you have rear drum brakes you don't have an "emergency" brake.
Rear disc's have small brake shoes inside the hat that is relatively small diameter for actual braking use, they're intending as parking brakes. Can you use it in an emergency? Sure, it's worth a shot since it is an emergency after all, but don't be surprised if they disintegrate before you come to a stop though, which is even more likely if the engine is still seeing throttle. It's not like older stuff that had rear drums where there was just a secondary mechanical linkage to apply the actual brakes meant to stop the vehicle.
And no, I didn't read all 5 pages of the thread.