When I try and visualise this i get the picture that your "pushing" the fingers into his arm.
/Yari
No, not pushing into the arm.
Visualize the hand, uke's, as a ball with the wrist on one side of the ball and the knuckles as the other end of a ball and a very finite point in the palm is the center of the ball. Now the ball is rotated around the center so the center point does not move in relation to uke/tori but the edges of the ball (wrist/knuckles) rotate around the center point. This is good circular motion and the smaller the better, meaning if the center point moves in space the circular motion becomes oval at best and most likely linear, it reduces the affect. The tighter the circle (think and feel three dimensional here) the better.
Another way to describe this is to think of tori's hands on the outside of the ball described above with the ring finger(s) in uke's wrist and the thumb(s) on uke's ring finger knuckle (shortest tendon on this finger so it reduces the amount of slack). Now keeping the ball in one place rotate it so the edges of the ball change places, i.e. the thumb rotates across the top of the ball then goes down and under while the ring finger rotates towards tori and up until then continues up around the ball and back towards uke. Notice that the thumb and ring fingers are 180 degrees out of phase. As one is going up the other is going down but the center remains the same. Visualize how such a motion transmits into uke's body (think basic geometry here).
Now to make it more verbally challenging; as you do this three dimensional circle do not do it straight back into ukes forearm/elbow but at an angle (about 30-45 degrees) to the outside of the forearm. If you can follow this description the affect on uke's ankle, knee, hip, shoulder, elbow, etc are rather profound. Remember to keep the circle small (Not the big motion morph4me mentioned).
Finally, joint locks such as kote gaeshi are to exploit a balance distrubance not to create one. Understanding this is key in being able to actually apply locks to non-compliant uke's. That and knowing which locks match each direction of balance distrubance.
Enjoy,
Mark J.
PS. One last hint. Tori, should never squeeze his hands. The hand should be in a comfortable 'C' shape throughout the technique, which mantains the correct shapes needed above and allows tori's arms to stay relaxed. Once tori squeezes his hands the shapes (ball & circles) are lost and the tension in tori's arms make it very difficult to move properly. The power comes from the hips. Although to be honest if applied with the correct balance distrubance it takes a minimum amount of power.