I suspect the "plank" is actually a wood veneer glued over a set of blocks. The veneers are extremely flexible (you could roll them up) and would look like this once carefully assembled. A side view of the 'plank' would be interesting.
I was just thinking the wood could be soaking in water for a few days to get it good and mushy, compressed and shoved through the neck via clamps. The knot you could tie (or partially tie) via thin shipbuilder's pliers. I have no clever thoughts on getting a metal nut or a lightbulb through the too-small neck of the bottle though.
