I wanted to share that I have found a third-party product to use as a "sports case" for Dexcom G4.
It is made by amphipod.
It is part of a series "Smart View". The micro size fits the G4 well. The beltpod version is the one that can be used with a belt (does not have a clip/clamp). There is also the version with a clip.
http://www.amphipod.com/products/holders/music/electronics/beltpod-smartview-micro
I had my G4 receiver in this case strapped to the front of my bike for a very wet, 3+ hour bike ride on Sunday. Worked great to keep the receiver dry and viewable during the ride.
The amphipod logo is a bit large (covering more of the viewing area than ideal) but I still think it works well. The logo is sewn in place. To remove the logo would leave exposed holes in the viewing area. I don't have a way to take a picture today of my G4 receiver in the case.
I am able to access all functions of the G4 while it is in the case. I only have to remove it from the case to recharge or download data.