10-dummy-monitor.conf

Section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy"
EndSection
Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync   31.5-48.5
    VertRefresh 50-70
EndSection
Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
        Depth 24
        Modes "1280x720"
    EndSubSection
EndSection