Summary

A simple mount for any model of the Raspberry Pi. Offers little protection but is easy to remove and insert the Pi.
Here's a video showing it in action: http://youtu.be/4OCn-_bs40c

Instructions

Print the 'clip' and 'holder' files as they are. I used PLA which is slightly flexible and helps the clipping system. I'm not sure about results with other materials.
Glue the clip onto the mount using epoxy resin (or similar plastic glue).
I've updated this so there are now two small lips in which to slot in the clip to the holder. I've also incorporated a small tolerance between the two components to allow for printers which are not well calibrated and also the glue.

Raspberry Pi Clip