This is a remix of the excellent 'Skeletonz' model from muzz64.
The only differences to the original is that I've scaled it up by 1/5th and placed holes for 5 9mm magnets.
The other magnets in the second picture are:
The original model suggested a denser infill and 4 shells - I didn't find that necessary, but YMMV.
When I printed it, I did rotate by 180 degrees so that the presentation side was downward on the print bed, but either orientation should work.
Gently work the joints after printing as they might be a bit stiff - you should hear a small click as they free themselves. If they snap or have completely fused, try reprinting with a lower extrusion multiplier.
I used blutack to hold the magnets in place which should work with both PLA and ABS (my print was in PLA).