Those should be online, if you want to do the legwork. In one of the
published cases, the Feds went after a CFI who was in the back seat at
the time of the incident.

The only case I can find is an *Inspector* who was the object of a
lawsuit, even though he was riding in the backseat. However, he was
giving instructions to the pilot, who was being evaluated, so there is
some legitimacy to the charge.

There are multiple other articles talking about "who was PIC", but
this riding in the backseat thing was never mentioned, even though it
would have been appropriate.

I suspect the concept of a CFI riding in the backset, minding his own
business, and being charged with a violation is an OWT.