John Riggs: "Whatever is safe."
This is the guy I want to train with.
I lean toward any of the opinions expressed that are similar to "You just go with it, the way you are going, whatever is safe."
If nage is a beginner he may not know that we are in a situation that could break my back or neck.
A good outcome, you should get uke resting his weight entirely on one leg and the other leg is at tip toe. At this moment in time, uke is probably arched backwards, with his head behind his center of gravity. The proceed with tsugi ashi (sliding) movement at a 45 degree angle across his arched back. Please note, as you slide, your hip is connected to the hip of uke.
I can imagine 'falling' backwards with the momentum, or jumping back and falling and countering the technique by bringing nage forward and turning to do sutemi waza. No?