using ActiveRecord with flat files

For the application I'm working on I would like to not save the uploaded files in the database as I have done previously. It seems more "natural" to simply store them in a directory. Now I'm thinking that it would be nice to be able to take advantage of ActiveRecord anyway - override a couple of methods, so that I can define the associations in the customary way and rely on the automatic saving features, etc. Has anybody done that? Which methods would I need to override? Or is this not feasible? Thanks. -Sebastian