Does anyone have experience with intentionally stalling the KOP servo (or similar servo) in order to provide a gripping force?
Are they forgiving about this or do they burn motors and strip gears?
Generally not advisable. It would be relatively simple to test it, and then post your results here. Worst that could happen is you destroy a servo. Better now than during a competition. You could get more force using surgical tubing. 
Thanks for the input.
I agree that it would be better to provide some spring or stretch in the linkage so that the servo can actually reach its taget position.