Digging into my string setup toolbox, I also found my neck rest
(I have made so many tools, I sometimes forget I have some ...)
The idea of this tool is not from me, it can be seen at several places on the net, and a commercial version is sold by Stewmac.
My version is made out of solid teakwood, waxed, and cork lining.
The beauty of this tool is that it can adapt to any size of instrument, and any neck angle (though this one is quite narrow wich is suitable for the mandolin family, which is my main preoccupation)