I like the idea of implementing the reward at the start rather than the end! It seems to make use of the fact that getting started is often the hard part of a task. Completing a pomodoro once getting going is pretty easy. (I often use a similar technique to pomodoros and very rarely fail to complete a block of work or avoid distractions during it. I'm much more likely to get too sidetracked during my "break" time and fail to start the next block.)