How about this?
http://www.flickr.com/photos/sinks/373267864/
I used this on a bike with an 1D and a variety of long lenses (70-200 2.8, 300 f4, 400 f5.6). The sideways strap is comfortable and the bag weighs next to nothing.
http://www.kgear.com/store/index.php/e/e970.html