You might try adding a server layout section and a screen layout section to the xorg.conf file by the same name as that user. The X server can be started with a -server or -layout option. I'm not certain on the best script or config file to edit, and sometimes it depends on the distro and whether you use a login manager or start with the "startx" command.
You might look at the /etc/X11/xinit/xserverrc or $HOME/.xserverrc file. On mine, I think I would test for $USER=username and add "-layout username" to the $args variable. Then when one of the lines:
exec X $dspnum -auth $auth $args
exec X $dspnum $args
runs , the xserver will use the layout argument.
Another possibility is to use SCPM so that a different profile is used for that user, and configure it so that a different X configuration is used such as a special /etc/X11/xorg.conf.username.
On some laptops, you may need to select the S-VIDEO output using a special function key that cycles through the video outputs. Also, on some video devices, you need to powercycle the laptop before a newly connected S-VIDEO output will get a signal.