Tie a bungee cord to a bike, just under the seat (figure 1) and then you could buy or make a wheeled cart with the plans that Zengineer1618 suggested. I know this is like, three years to late but I was googling the same thing and this popped up, but I was also googling it to do something else with the cart, as I was going to make it into a seeder/transplanter. Just hook the cart to the bike with the other end of the bungee cord. As substitute to the bike you could use a motorized bike or golf cart, ect. I hope this helps!