Is it possible to ad the second disk without losing data in the first disk, and is it possible to auto delete files which are not accesses for two weeks ?
While I know videocache supports multiple cache directories, I strongly advice using some sort of volume manager at the OS level to aggregate disks.
One solution would be using Veritas Storage Foundation.
Their basic license is free (up to four volumes).
Another solution would be LVM or any other volume manager that comes with your OS.