i can do this, its not very hard, but you have to get the right feeling
try to walk backwarts and put your leg next to your support leg (at the other side than the normal way of course) if you can do this well, try it with a ball, just kick it against a wall (not too hard) and try to do the steps over the ball. if you master this you can try to roll the ball backwarts yourself just as the guy in the vid does ;) i hope i helped you with this
