This was designed with the help of Team Unlimbited (http://www.teamunlimbited.org), and can be printed and assembled by following their instructions. A video of it in use can be found here: https://youtu.be/LmcIhVnmvjw
The big difference is the hand, which has no fingers. The hinge can be completed with a piece of filament as the pin, just use something hot to make the ends slightly bulbous so it doesn't fall out. Better to use 3mm for the hinge pin, 1.75 will be a bit loose (but also works in a pinch).
The cover to the bow holder snaps shut.
One small thing: The person this was made for plays the cello mirror image of other cello players. It is possible you may need to move the rod that goes in the bow frog for a standard cello player.
Iteratively, with the end user