I'm deeply fascinated with the idea of onboard video. Which is why I too, just ordered one of the keychain cams.
I also am getting ready to start a 6 inch diameter upscale estes alpha. It will be dual deploy and I will have a mounting rig in the Ebay to hold my Nikon. I will also put a mirror hood on the outside. Adds a weird little piece onto the rocket, but in turn I get good HD video of the liftoff.
Essentially it is a simplified version of Vern's module on starfire, which can be found
here. I won't be using the fancy wiring, I'll just turn the camera on, press record and stick it in the payload bay. I'll cut the walking to the pad out of the video.
I built it around the Loki 76/3600 case that it will push it to over 6K with the standard L motor. That however will be a ways off. First we are going to fly it on a J350 for my Dad's level 2 cert.