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.
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script to do this quickly
Is that a request for a script?
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BTW, to get a start making the fingers, you can draw a curve along the edge, and then divide it.