The wooden peg mandolin device might be the Cremona style.

The Cremona mandolin attachment consisted of a wooden tray that is
mounted just below the hammer line.  For each note there is a thin
wedge of wood (usually maple) that is spring loaded and just long
enough to fit between the shank and the strings, with the hammer
touching the strings.  A pneumatic on the side of the piano action
moves the whole assembly to the left and the wooden pegs line up with
the shanks.

When the hammer hits the strings, the shank hits the wooden peg and
taps the wedge into the strings.  The springs have to be just the right
tension to keep the wedges back.  It's not an easy one to build from
scratch!

There were probably a dozen different mandolin attachment designs
throughout the production period of coin pianos and orchestrions.  My
favorites are the ones that are made with wood as the point of contact.
There are some good ideas in Craig Brougher's "Orchestrion Builder's
Manual."

Brian Smith