Scheduled Backups: what about 5th week?

[typneun]

we are a small design agency and work with a G4 as our server, with os x server (tiger) running. superduper is used to do the daily smart backups of our data-raid onto a firewire-harddisk.

so, our problem is: we have two firewire-disks, and we want them to change every week. so that in week 1 disk 1 is used for the backup, in week 2 disk 2 is used for backup, in week 3 disk 1 is used for backup, in week 4 disk 2 is used for backup. OK, so far everything is fine.

but: what about next week? it is definitly the 5th week of the month, and super duper doesnt count to the 5th week - so that the next scheduled backup after tomorrow is on the 3rd of july.

what should i do? is our backup strategy possible using superduper? thanks for your help!

typneun