Nice! How about also adding a vibrating cock ring (or a few of them) around either the base of his cock and balls, or around the cage somehow? Although around the cage may be difficult with this cage due to the circular rings and all of the spaces in between. Then a warning that if he cums there will be a penalty. Maybe that means the key is moved further away or into a more awkward place, or maybe a ratcheting rope from his tied balls to the bottom of the cage, as @bgpcf mentioned, gets cranked down A LOT lower for a 30 minute penalty if he cums. More incentive to NOT cum, and to instead just try to deal with the frustrating distraction of the BUZZZZZZZ of those vibrating cock rings designed to make him mess up from lack of focus on the task at hand. Errr, the task at mouth. ;-) Whatcha think?