Magnet D20 - Always Roll 20s

Pause the print when it starts printing the hollow area. Insert a 40mm diameter / 20mm height rare earth magnet. Unpause the print.

Make sure you are rolling on something that is made of ferromagnetic metal.

Always roll a d20. Doesn't last long, until the DM inspects your d20 and can feel the weight distribution. At this point, it may be best to just run away with no explanation.