If by "Backup the Backup" you mean create a copy of the Disk backups on tape, you need to create DUPLICATE jobs rather than COPY jobs. This will create new catalog entries so that you can restore directly from tape, rather than having to restore to disk, then restore the data
You can use POLICIES to do the Duplicate to tape. Directions are in the Admin
Guide
As long as you do not partition the library, and point the DUPLICATE jobs to the All Tapes pool, it should grab the oldest scratch tape in the library and continue on the next oldest as needed