Sorry, but I don't really have much experience with this sort of thing
(I haven't really worked on a rails app in a few years). I'm not sure
that there is a direct way to do what you want to do, I think you may
have to make separate models and manually integrate with fog but due
to my lack of experience with Rails I'm not sure. I had hoped
somebody with a bit more knowledge might be able to help (hence why I
waited a few days to reply).
wes