I used to own a TTZ so I still go to this site. This member has created a little trick. By reading it, it looks like it only works with white faced gauges though. Check it out....
http://www.twinturbo.net/cgi-bin/ttnet_viewmsg.pl?forum=general&msg_id=126629
http://www.twinturbo.net/cgi-bin/ttnet_viewmsg.pl?forum=general&msg_id=126629