While there are several Mac backup programs, apparently only Retrospect from 
Dantz is designed to backup to CDR. With the cost of blank CD's being so low 
and CDRW drives with speeds up to 40x this is the best way to backup several 
gig of data. Unfortunately the only competition for Retrospect that I could 
find, is Backup Mastery from Charismac, but it is temporarily unavailable 
until version 2.0 is released.

Is it possible to write a backup program designed to work with CDRW drives, 
with FB^3?

I would think if you integrated it with Apple Authoring Support that the 
trouble of keeping up with the different CDRW drives would be eliminated. You 
would need to be able to copy files as large as 2 gig, use compression as an 
option, do incremental backups, and spread the backup over as many cdrs as 
needed even breaking large files into pieces so that they will fit. You also 
need a verification process.

Bruce Moore