Well, another easier way is to perform client-initiated backups using scripts.
Since the file list is changing in a very standard manner (one dir per day), it might be much easier to write a script to perform a manual FULL backup of today's and yesterday's folders daily.
For eg : Get date field from the OS, and create a backup list with year/month/today and year/month/yesterday and use bpbackup from the client to back this up.
Once you are confident that the script is working fine, you dont need to take even ONE full backup of the ENTIRE filesystem.
Regards,
Karthik