This will probably be a quick 'no' - but it's worth asking anyway. Just got a 48 spoke 20" wheel but realized when I got it that it didn't have a coaster brake. Is it possible to swap out the existing hub or does it require rebuilding the whole wheel? If it requires rebuilding what about turning this freewheel into a fixed wheel? I checked out Sheldon Brown's site but I wasn't totally sure if it was possible or not.