Wow honing a shim is kind of anal, that's why the factory gives an acceptable range
Get a rubber ball, or a "stress ball" if you are really weak, and use it untill you get fingers working some. Some suggest boobies will also work when the cast is first removed!
Remember that the squeeze thingy is supposed to be curled between the compression and the release...
Wrist out straight-compress, bend wrist-release, keep wrist bent-compress, straighten wrist-release, keep wrist straight-compress, bend wrist-release, etc. don't forget to work the good hand/wrist as well