Does anyone have plans, or tips on how to operate a dummy's dummy. I'm sure there are various options so any ideas will help.

I've built a few of these for clients over the years, with varying methods of operation and complexity. The simplest involved a tube coming from the back of the mini-dummy, which would plug into a hidden hole in the body of the larger dummy (when not in use, the hole was hidden by a jacket the larger dummy was wearing). The control for the little dummy was basically a string running thru the tube with a ring tied to it.

It was a simple setup, but worked quite well for the short bit my client did with it.