One of my aikido teachers taught nikkyo osae and sankyo osae as stretching - never pressing down on uke's shoulder but just twisting uke's are over his/her head, with the feeling of lifting rather than pressing. Very pleasant for uke, and he stressed that.
this is how I have been taught to perform the ending of these techniques. They are very good way of providing a theraputic stretch to the shoulder joint, as long as it is done in a controlled fashion. Uke signals the point of stretch end by tapping out.
I can't imagine practicing any other way, at this point of the stretch, uke is already immobilised, so the 'martial' part of the exercise is complete. Why go any further? Any thought of going further to cause damage, is not aikido in my mind.
If you want to perform dislocation in nikkyo osae and sankyo osae. How do you do it?
Don't stop when they tap out, just keep right on going