A simple GoPro mount that is placed around the rubber in front of the eyepiece and then is clipped into place as in the picture. It was originally designed for a specific cyclope, however I tried it and it worked on the 2 others I could get my hands on.

The attachment point was remixed from a GoPro mount on this site with the filename GoPro_pin_system_UPDATE.stl, however I can't find it.