BESR 2010 Backup destinations

I have 3 USB drives used as backup destinations, let's say drive A, B & C. Drive A is used for backups on Monday and Wednesday. Drive B is used on Tuesdays and Thurdays. Drive C is used on Fridays.

I created the backup job with drive A and haven't found a way to correctly add the other drives as storage locations for the backup job. I've had to change the backup job to use drive B, then the backup job won't run when drive A or C is plugged in. How do you correctly assign all 3 drives to the one job?