I wonder if he would have been better off making a device to hold a small mirror steady and used a telephoto lens pointed at it from one of the f holes.
It says he had a 5 mm hole to work with. That would pass an 8 gauge wire with plenty of room to maneuver. Mount a mirror to the end, thread a two or three foot wire through the hole from the inside out, clamp it to a surface the instrument is sitting in to keep it from moving, and set up your camera from a low angle and the light positioned to not cast a shadow.
Alternately you could J hook a long, large diameter scope, and composite two shots with the cable visible on opposite sides of each picture.
It's an interesting idea - and I have played with using mirrors. But I run into a few problems:
Most mirrors will actually show a faint double image due to the silver being behind the glass. This becomes more pronounced if you're shooting at a steep angle. Single surface mirrors are pricy, and finding one that could slip through the f-holes of a violin is a challenge.
Also - if you're outside and pointing in, you're running into some similar issues - the f-holes are simply too thin to telephoto through without them blocking image at least partially - and then you're no longer shooting wide, so you wont see much of the instrument in the reflection anyway.
It says he had a 5 mm hole to work with. That would pass an 8 gauge wire with plenty of room to maneuver. Mount a mirror to the end, thread a two or three foot wire through the hole from the inside out, clamp it to a surface the instrument is sitting in to keep it from moving, and set up your camera from a low angle and the light positioned to not cast a shadow.
Alternately you could J hook a long, large diameter scope, and composite two shots with the cable visible on opposite sides of each picture.