Just some thoughts
Just thought I'd share my thoughts.
With many techniques there is a very fine line between having an injured joint, and having nothing at all. This is a big reason for cooperative practice - avoiding injury. Unless you are confident in the amount of control you have, you shouldn't seek to reverse techniques against an uncooperative uke - except if you're specifically practicing that way.
When I've encountered such situations, sometimes I remind the uke that it's easy to resist if they know what technique is going to be used, but that 'striking for distraction' can be a very effective way for me to momentarily take their mind off the idea of resisting - during which time I can slam the technique on. They usually get the idea. If not, when he resists, I focus a strike at him - I don't even have to make contact but a kiai helps the effect, and he softens up for an instant as he anticipates being struck, during which time I complete the technique. I point out how well it works and tell him to just imagine how distracted he'd be if I really had struck him. I also explain how I could use a strike to amplify the pressure of the technique I'm attempting to execute, but in doing so control would be compromised and this would likely cause injury. They usually understand now that their resistance is meaningless.
Either that or I'll make him permanant uke and pair him up with advanced students. I explain that being uke is where you really learn to get a 'feel' for the techniques if you try, and that he should learn to be a good uke. This is good for the advanced students too because, as has been discussed, it challenges them to harmonize with uke in order to find an effective technique.
Usually, to start, I just tell them to stop resisting because it's not what we're doing right now.