When I went skydiving, the guy had a Rebel XTi with 18-55 and a high def compact video camera on his helment. I don't know any details how it was mounted but, he used a mouth trigger. It would be similar to what a water camel pack would be, you bite the tip and it takes a picture.
The pictures came out great. All you would have to do is set it to focus on the closest subject.
There is enough contrast between the sky, the jumper and ground that the camera will be able to focus. He also put black duct tape on the lens to keep it from rotating. Looking at my pictures, I don't think it was set at 18mm, its be too wide.
~Michael~