Hmmmmm... That is an interesting question. Especially when you consider that DV video takes up 3.3 MB per second, and a standard DV tape can hold 60 minutes of video... Theoretically, you could fit nearly 12 Gigabytes on a single tape. And since each tape only costs a few dollars, you would have a very inexpensive firewire backup drive.
I doubt that the software exists to let you do this right now, but perhaps some brilliant young shareware developer might read this and be inspired to write such an animal.