Messing around with the M5 Atom Echo I just bought for my Home Assistant Server and realized it's pretty light and doesn't really stay in place on it's own.  So I drew this up in Fusion 360 real quickly and used the negative volume object in Prusa Slicer to create cavities for pennies to help weigh this down.

The 3MF file includes a filament change at the correct layer so that you can put your pennies in.  You can reload the filament after or change out to a different color.