Handy dandy video from the University of Minnesota.

For each tire you’ll need two tubes (one will be sacrificed), about 120 1/2″ wood screws, an awl, scissors and plenty of time on your hands. The basic process: punch holes in the tire, screw in the screws with the tips facing out, and use the sacrificial tube as a liner to cover the screw heads on the tire inside surface. Position the screws on the cornering tread.

If you already know how to deflate the tire and remove it from the wheel, skip ahead to 2:30 after you get past the introductory material.