You could try wrapping them for the winter (see the numerous "winterizing" posts. In your case being in a container, you will need to protect the roots well. Maybe wrapping the container (sides and bottom) really well. Some folks have used a string of christmas lights to provide some warmth when the temp goes below freezing. I have a container fig I was thinking of keeping outside this winter as well. I'm in zone 6a and we get some really cold weather over the winter. I think you will also need to have access to the pot to provide a little water about once a month so the roots do not dry out.

Why not bury the pot and cover the top with leaves, or bury the whole thing? (If you have the space)
Ox