I was put on the spot tonight, and when I tried this it ended up in either iriminage or kokyunage because of muscle memory, I suppose.

After a few minutes of practice it came back to me, thankfully.

Uke comes in as usual, but with a little nagare he can’t quite get behind you. Just as you let him touch the second wrist, twist your hips and guide your grabbed-wrist over your head bit hugging the form of your head. In other words, don’t let your arm go behind you.

Slide back a little and extend out your grabbed-arm like a blade cutting something in front of you. Extend Uke so he is a bit off balance. At the climax of your extension, slide back some more to go more beside Uke but still in front of him.  At the same time change hands by sliding one hand up his arm while the other hand contacts his head with a firm grip near his nerves.  This all happens smoothly and in one motion. Continue like a basic kaitennage.

I practiced this with about 6 people tonight, and even rock-solid Andy got moved gracefully :)

I watched beginners try this for about 20 minutes so I could see many attempts. I saw that if Nage cuts down and steps back without extending his arm first, then Uke can escape with a quick turn.