I was goofing around the hump yard, pushing 2 tankers and a box car, I successfully uncoupled from the locomotive from the cars on the fly. Using the shift 3 key to be on the ground very close to the cars. I unlocked the car.
They proceeded to roll rather far down the yard. ( way too far and too quick). Maybe with the right brake wheel tension it could slow to a safe speed.
You can also control the loco from the rear of the train. Need to experiment much more.