The reward technique never works with me. Because, to me, there is not 5m doing something fun. I cannot have something really fun in 5m. So I rather finish all the things in limit time and enjoy the rest of the day, it's the biggest motivation. My only work solution to get back to the flow quickly is leaving something undone. Depend on which task, it will have different ways. Btw, I really love the idea of leaving failing test :D