Imagine ryotedori kokyunage with a tenkan and a slide in for a kokyu-armbar-nage. That was this technique, except Uke grabs the shoulders instead of each wrist, and you have to duck under and between his two grabbing arms for the extension. Then you do a forward ukemi to your knees to generate the sufficient momentum to throw off-balanced Uke.

You can either slide off the line and step back, of you can slide off the line and forward. It depends on how much time you have and how aggressive Uke is.