ATI

Nuke all the deprecated cruft from the xorg.conf file. So that's the HorizSync and VertRefresh from Monitor sections, and any manual Xinerama or dual head configs.

Add a Virtual line to the Display section:

Section "Screen"
    Identifier      "Default Screen"
    Device          "ATI 200M"
    Monitor         "Laptop Display"
    DefaultDepth    24
    SubSection "Display"
        Modes       "1280x768"
        Virtual     2560 768
    EndSubSection
EndSection

Then use xrandr to wake up the other end of the DBUS cable and clone to it:

johnno@jonlap~$ xrandr --output VGA-0 --set load_detection 1
johnno@jonlap~$ xrandr --output VGA-0 --auto 
johnno@jonlap~$ xrandr --output VGA-0 --mode 1280x768