We found these two videos that introduce us to an training accessory that claims to help you improving, or learning, the drag flick. The Sleep Push basically consist on a ramp that can be placed on top of the circle and will help you carry the ball across the elevated surface giving you an easier sensation of the drag flick motion.
This video, shows you exactly how it works:
In this next video, we can watch a full training session making use of the Sleep Push. You can see how players of different level seem to enjoy and see improvement with this tool.