You can extrude the fingers inward, and do a boolean subtract.
If you are making box-joints, you will need to have some thickness.
In the case of the dodecahedron, it may not be easy or even possible to get a physical result that can be assembled/disassembled.
script to do this quickly
Is that a request for a script?
BTW, to get a start making the fingers, you can draw a curve along the edge, and then divide it.