Bill, if you can get me a video of this, I'd love to try it. I think I am lacking in some mental ability in translating words to physical actions, but I love a good nikkyo. We have quite a few super flexible young men we train with, and pain compliance on some techniques is hard to come by. I've got one that I refer to as "the fancy nikkyo" that works with pain compliance on all of them, and I'd love to learn another one.
The hand you're holding their hand with stays the same. The key is to rake the top of their forearm (really, the bottom of their forearm, which is turned upward at that point) with the bottom edge of your's, (toward you) instead of grasping their wrist. You know the lightning bolts you get from yonka jo? Uke will follow you to Japan, trying to get ahead of this one. Sorry I don't have a good .gif to offer. If you practice it once, you will figure it out.