My mother in law wanted a magnetic pincushion, so I whipped up a quick tray to use as one in Fusion 360.

It uses 5 embedded 8x3 disc magnets.

To embed the magnets set your slicer to pause at the layer where it closes over the void for the magnets.

Based on the calibration of your printer you might want to scale it up a bit if you find it wont fit, but on mine they dropped in but stayed snug.

Check out my other models here