Update, July 19, 2015, v1.0.5. Added an additional rotate parameter, allowing you to mount to a vertical tube while keeping the goPro oriented properly.
Also added pre-rendered STL files, for those that didn't want to use OpenSCAd or the customizer.
This clamps to a tube/stick/pipe and has options of a standard GoPro tab mount with bolt hole, or a new quick-release buckle style. Fully configurable.
If there's a dimension that you need to configure, but can't - let me know, it would be really easy to tweak or expose other variables.
Open with Customizer, and then build it twice, once for the top and once for the bottom (with same settings otherwise). The preview mode is great for adjusting settings and seeing results, but cannot be directly built - only one part at a time.
The main options are to choose the type of mount, whether it is rotated, and then the diameter of the tube for the mount.
I've also made the clamp bolt dimensions adjustable, the defaults just fit some bolts I had lying around.
All of the other parameters are configurable but hidden, so if you're advanced, download the opens cad file and have fun!