A recent addon for blender that allows the user to draw over the mesh and it cuts it like a cutter is really awesome. It’s called freehand cutting. The very first image in the about section of the store page shows it. I’ve attached the link to the addon page below.
Imagine you draw a curve on the shoulder of the character; it snaps to the mesh, and you have the ability to extend the curve and edit it. As soon as you make a complete 360-degree rotation around the shoulder of the character, the curve loop closes, and the user gets the ability to split it. That would be awesome.
Right now, the best we can do is add facegroups and split the model, close the holes, and make the pegs/keys.
Please take a look at the link for blender addon, the store page has images, that will give you a good idea.
Split-3DPrint - Superhive (formerly Blender Market)
I know this may sound too optimistic but I’d love to see it in a future release someday!