This has been on a long quest, but I finally have my phone mounted on my bike the way I want to.
I always thought it was stupid to have the phone(or bike computer) mounted way below field of sight. Now I addressed this in my carbon fiber mount. I also dealt with flimsy construction aspects of bike mounts(had a couple of commercial mount eject my phone)
I made the case out of carbon tow held together with paper tape :). It came out a little flexible, so i could bend it to get phone in/out. I was going to devise an elaborate locking mechanism for it, but carbon ended with the right mix of flexibility/stiffness(yay luck)
Here is a video of me stress-testing it. E71 sucks at video :)
And some video of the mounting mechanism. SLR video is sexy, even without AF.
Anyway...hit a teeny teeny snag. Turned out adding the carbon attachment loop to the case had an unexpected effect. I wrapped it on with some more carbon tow and cut off the tow that covered the screen area(once it dried). This made the case not flex anymore. It became extremely stiff. So once I put the phone in for a testride, it didn't want to come out anymore. Carbon is so unintuitively easy to stiffen up.
Now the case is a slider. It is still extremely stiff(but 1.3 grams lighter). Since I made the case by using my phone as a mold, it fits it extremely snugly. I might add a little bendy stopper bit, but so far it seems like overkill.