Not so stupid...
It should work just fine. Coffee grinders are just rapidly spinning blades in a confined area. A small food processor, especially one that has small bowl insert to help keep things together, does the same thing.
Another trick I saw in Charlie Craven's book is mixing the dubbing in a plastic sandwich bag using canned air to get it spinning around. Let me know how it works out, because I have an old processor sitting in the attic waiting on our next garage sale.
......because the voices in my head tell me to.”