The easiest thing to do is to is to use a utility like DirectCD, and format the disk. That way, instead of "burning a CD" as a backup method, you are "backing up to a backup file".. that file can be on the DirectCD disk is simply a Rewriteable in your burner drive.
The DirectCD-formatted CD is treated like any other hard drive, network drive, or floppy drive. Once the system recognizes it, it will allow you to read and write to it like it was a floppy.