VTL for NDMP only: How to reclaim space on the Data Domain?

We have a DD4200 with OST and VTL.  The VTL is for NDMP only, the VTL Drives are connected to the Backup Accelerator Device connected to the EMC ISILON NAS.  I tried quick erase but seeing as the media server doesn't really control the tape drives. it failed.

How can I reclaim space from the VTL tapes on the DD4200 if we only have NDMP drives? 

Thanks