Dave, LISTSERV is not the only kind of program to respond to operator
messages.  The problem really lies not in the server, but in the message
and its source.  If it is the case that you have EXECs that send these
messages, you simply need to add an asterisk to the beginning of the
message text, and ANY server that obeys the now defacto standard will
not give a response or otherwise react.
 
What do you operators think of any "*GONE but your message has been recorded"
messages they might receive, or do you not let people be in DISC with GONE?
 
Still, a list of IGNORE userid (with nodes in the syntax, too) can be a
nice feature for quickly solving various kinds of message problems that
pop up.  I just pointed the above out just so that you might try a solution
that kills more than one potential problem.