It's pretty rad that Mountain Lion allows multiple disks to be added on a rotating backup basis. But here's my problem: I have some smaller external HDs I want to create extra backups on. They aren't big enough to hold my entire original backup. (I thought they would at first glance, but Time Machine requires extra space to work.) Is there a way I can use "Exclude these items from backups" to selectively exclude really big folders just for these disks?