It is possible. I have made an external command helper in my script Date Calculator which uses a hard-coded array of command parameters. You may want to twist it a bit with the AutoComplete class to allow for dynamic arrays and there you go.
Popup ListBox - by 7d5 on 10-30-2008 at 09:02 PM RE: Popup ListBox - by Matti on 10-31-2008 at 09:17 AM RE: Popup ListBox - by 7d5 on 10-31-2008 at 10:32 PM RE: Popup ListBox - by Matti on 11-01-2008 at 08:00 AM RE: Popup ListBox - by SmokingCookie on 11-01-2008 at 02:16 PM RE: Popup ListBox - by 7d5 on 11-07-2008 at 10:45 PM