First I found a bolt the same size as the hole you mount a camera to a tripod with.
Shaved down the head to about 1/16" (0.0625in.) that should allow a stiff enough piece of flat stock for the part that grips the shoe.
Trim off the tab on the end and round off any sharp edges and its ready to drill the hole for the bolt.
If you look closely at the last picture you will notice that the first piece that I will be cutting off doesnt have the two bumps on it. That is good as it would interfear with it sliding under the shoe.
A little edge cleanup and the mount is made. Add a nut to secure the top camera and its ready for action.
Im using an old digital that I had in my electronics junk box to show how a camera mounts only. Ihave to use my good camera top take the pics with. The old one still works, but the resolution is atrocious.