Summary

Inspired by Sneakypoo's work, I ended up remodeling from scratch to make this. It's a handy pair of... jaws?... for holding PCBs during soldering or other work.

Also discussed here: http://www.makersite.com/blog/2013/5/2/magnetic-pcb-holder-nylon-printed

Instructions

Slice 'n' Print! I used Nylon but ABS or PLA would be fine. After slicing, visualize the gcode (using Netfabb or Pleasant3D or similar) and figure out where you need to pause it to drop your magnets in. I use Sailfish firmware and use the Pause and ZPos feature.

The cavities meant to hold the magnets begin to be capped off at a height 3.34mm above the base plane (assuming you're orienting as I did for printing). That should help you decide where to pause... but do double check, as there are sometimes tricks about starting elevations, etc., depending on the slicer settings. (Thanks, Austin!)

The magnets are neodymium, very strong, 0.5" diameter x 0.1" thick disks.

Magnetic PCB Holder - Embedded Magnets