VCB snap of only the System disk of a vm.

I am using ESX 3.5 VC 2.5 and Avamar as my backup.  I am doing some backups using VCB 1.5.

I have some vm's with a 20gb OS disk and 500gb data disk (linux).

I would like to do VCB of only the OS Disk of some of my vm's and not the other much larger data disks on the vm.

Is there a way to only snap (one disk) the smaller OS disk of the VM so I don't have to have a VCB temp disk that is huge?

I also don't want to wait to snap 520gb just to get the 20gb I need.

I realize Avamar can filter to only grab the 20 but that is after the snap, I just don't want to snap the 500.

Thanks