Capreo hub is probably your best option. The hub you will need for sure as it the only on that will take a 9 or 10 tooth cog.
You could try a Schlumpf Speed Drive internally geared bottom bracket.
http://www.schlumpf.ch/antriebe_engl.htm However that would probably require a LBS experienced with it to install it as you may need a special tool and I am not sure it would work on a BF.