I have made a little Focus Ring holder for both Cpro and Hi-5 Focus Rings.
There are two versions with different mounting options.
One attaches permanently to your Robocup and the other one uses a little dovetail by @Cédric Heckly to get it off easily and store it away.
Both use the standard velcro straps that come with the Robocup.
If anyone needs a version that holds more or less rings, let me know.
Everything can be printed without supports and all you need to assemble is two little M3 Screws.