I haven't seen this suggestion yet, but when we have a need to write to
a tape outside of NBU, we use the tpreq command to mount the tape in a
drive, write to the tape, unmount the tape using tpunmount. 

For example, I might use the following sequence:

/usr/openv/volmgr/bin/tpreq -ev 123456 -d hcart -p scratch_tapes -a rw
-f /tmp/tape.jlf
tar cvf /tmp/tape.jlf /stuff-to-tar
/usr/openv/volmgr/bin/tpunmount /tmp/tape.jlf

This works in NBU DC 3.4 and 4.5

-- 
Jack L. Forester, Jr.
UNIX Systems Administrator, Stf
Lockheed Martin Information Technology
(304) 625-3946