Working with Andell, we figured out to make the final gokyo osae when Uke has his arm locked straight out. Ben Sensei did this to me once months back and I remember the pain I caused myself from resisting (at his request).

Since Uke has his arm straight and locked as in the ikkyo osae, why not hyper-extend his elbow first by pressing on his elbow and raising his wrist? His wrist will leave the ground by a few centimeters. Suddenly, if you pull up on his sode and push inward on his wrist toward his elbow, his arm will surely bend.

If Uke reluctantly goes into gokyo, but maintains a fist and locked wrist, you can simply push on the wrist, or pop it, and it will collapse.