If you are only trying to dump Netscape users, try this instead:
netscape -display x.x.x.x:0.0 -remote 'openURL(file://evilmsg.html)'.
You can get the display using "ps aew <pid>" (the w adds another display line to the ps; more than one w may be needed - ps aewwww - to get to the DISPLAY env variable). Put a little web page in evilmsg.html. This command will find the first netscape running on that display and execute that the "openURL" command and display the evilmsg. Then you can delay a few seconds and then kill'em.
See this web page for more info on what can be done.