That would make a great predicament jimmycontour. I like the idea. What if the dildo is a vibrator as well? Sounds to me if we got together on this we'd need a separate generator :) 
But going back to your idea - lowering himself to provide relief, getting max vibes on the dick, raising himself reluctantly, repeat until he makes the error of not doing it fast enough and spurts, then has to put up with it all continuing for x time albeit with that feeling of having cum - and it's no longer so much fun, well not for him. I'm happy to watch.