intel without connected monitor

[strawks]

Hi all,

I have a motherboard with an intel G45 chipset.
When I try to launch an X server with no connected monitor it fails with
(other outputs are ignored according to my xorg.conf) :

(II) intel(0): Output HDMI-2 using monitor section Sharp Aquos
(**) intel(0): Option "PreferredMode" "1080p"
(**) intel(0): Option "Enable" "true"
(II) intel(0): I2C bus "HDMIDDC_C" initialized.
(II) intel(0): HDMI output 2 detected
(II) intel(0): EDID for output HDMI-2
(II) intel(0): Output HDMI-2 enabled by config file
(WW) intel(0): Unable to find initial modes
(EE) intel(0): Output HDMI-2 enabled but has no modes
(EE) intel(0): No valid modes.

I have read how to setup dual head at
http://intellinuxgraphics.org/dualhead.html and my xorg.conf relevant
sections look like this :
Section "Device"
        Identifier      "Intel GMA X4500HD"
        Driver          "intel"
        BusID           "PCI:0:2:0"
        VendorName      "Intel"
        BoardName       "G45 [Intel GMA X4500HD]"
        Option          "AccelMethod"   "EXA"
        Option          "ModeDebug"     "true"

        Option          "monitor-VGA"           "ignore"
        Option          "monitor-HDMI-1"        "ignore"
        Option          "monitor-HDMI-2"        "Sharp Aquos"
EndSection

Section "Monitor"
        Identifier      "ignore"
        Option          "ignore"        "true"
EndSection

Section "Monitor"
        Identifier      "Sharp Aquos"
        ModeLine        "1080p" 148.50 1920 2448 2492 2640 1080 1084 1089
1125 +hsync +vsync
        VertRefresh     23-61
        HorizSync       15-68
        Option          "PreferredMode"     "1080p"
        Option          "enable"            "true"
EndSection

Is there a way to force the driver to use the 1080p mode even when no
monitor are connected?

thanks in advance.

regards,
strawks