What you'll want to do is to duplicate the images back to your disk storage unit, and you can do that from the catalog section in the administration console. Go there, and change the action drop down menu to 'duplicate' from 'verify', and then put in criteria to describe the backups which you want to duplicate, those being the images you want to restore from. Once you enter in that criteria, click search now. Now from the list below, select the backup images you want to duplicate back to the disk, you can control click to select multiple images, then with those selected, go to the actions menu at the top, and click on duplicate. It will ask where you want to dupe them to, and you can specify your disk staging unit.
Caveats:
NetBackup has a default maximum copy value of 2, so since we would be duplicating from a second copy to make a third, we may need to increase the maximum copies value. Check the master server host properties -> Global attributes -> Maximum backup copies.
The images will maintain the existing retention, so be sure to either expire them when done, remember to use the -copy flag on bpexpdate, or you'll expire all the copies.
-Sean