Somebody in the Yahoo Brompton group cut a B bag frame down to fit a Ortlieb pannier (mounted the pannier much like you do on a rear rack). The frame was made narrower first so that it had the same width as the Ortlieb pannier. I fear that you need to be a member and logged in to see the pictures:
http://groups.yahoo.com/group/Brompt...02377/pic/list