Here is a solution for those trying to figure out the best way to create a Shoulder rest pad. Just uses a plate with a contoured foam shoulder rest pad for a violin. Cost for the pad about $3-$5.
More about the total build for the rig at: http://zehphotoblog.blogspot.com/2011/09/diy-dslr-shoulder-rig.html
a Photozblog.com production