I have tried several variants of this process. As expected, the largest road-block has been part 3 - the self-control not to consume the reward despite lack of completion.
I will mention that on the few occasions I have gotten this to work, my excitement and enjoyment was much higher than average. The desire and excitement for food seemed to translate into the task at hand.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.