Materials Needed:
60x10x3mm magnet, preferably neodymium/very strong
A little bit of super glue, depending on the tolerances of your printer
3x5" sticky notes
A pen, preferably with metal in it/metal case
Instructions:
Insert a pause in your print just before the magnet gets covered (check preview to find the right layer)
Put the magnet in the hole, along with a drop or two of superglue
Enjoy!
IMPORTANT: Do not use supports, the hole in the model is for the magnet
The author hasn't provided the model origin yet.