Get a long piece of clothes line or rope. Run it around the tire, following the center of the tread. Tie a knot in the ends, and stick a piece of pipe or a rachet under the knot and start turning it. Twist the slack out of the rope and draw it tight around the tire. The rope will press down on the center of the tire and it'll force the bead out towards the rim. Add some air and the bead should catch. As soon as it does, remove the rope.