A little redesign of the cap holder after some suggestions of my father :)
Hoping to making it simpler and more practical.

The bottom and perfectly flat face will hold the cap, even more, thanks to a sort of lip like the original thing (due to the first layer being usually more squished than the next ones); while the support, once removed, will leave a sort of grip on the attach.

Supported diameters : 40.5-77mm for the common known diam. (52mm in the pictures)

(If you wonder about the file name: "s" mean "support", because the initial versions were without; while "p" is for "pente" because the side is not straight for a more pleasant contact when grabbing the cap.
Here is also a 80sec. making-of the 49mm holder http://youtu.be/jQms74oR9hY )

Before print :
1) Set skeinforge for two shells and low infill, or even better if filled with shells and zero density nor solid surface to make a more flexible attach (like 15 extra shells)
2) Enable support (e.g. : Interface feed 2.0, flow 0.9, density 0.10-0.15, LTOLT 0.5, layers 0, lift 0.25; Support flow 0.7, gap 0.5, exterior only).

After print (10-20min) :
3) Remove support
4) Just slide it on your strap, shirt, or anywhere else :)