Thanks for all the responses.
I was not looking to experiment with other styles, just interested to hear how the technique is conceived and taught in other schools.
I can't follow the more esoteric descriptions here, but good for anyone who can.
Learn how to lock the wrist without applying so much pressure that uke feels pain. When you get there, consider how to lock the elbow, also without pain. From there go to the shoulder, or skip the shoulder and go to their center, or skip their shoulder and go to their front foot.
Yes, this is what we are practicing in the kenshusei course. As far as I can tell so far, avoiding wrist pain and going for connection with the hip, knee, or foot involves not trying to apply a technique at the wrist. Once you grasp uke's hand and forearm, if you keep good posture and just slowly lower your center, you can force uke down slowly without pain without moving your own hands, arms, or body much at all. This is maybe a very Yoshinkan way of looking at it, though.
After having felt both painful and non-painful versions of nikajo, I would say that while pain compliance might be an effective self-defense technique, the other is probably better aikido.
I'm not sure I buy the "pain is a secondary effect of the technique" line.