HP ProLiant with Ubuntu 16 and no monitor, using iLO remote console: screen size only 640x480

I have a HP ProLiant MicroServer (HP 819185-421) with Ubuntu 16.04.1 and no monitor plugged in, and I use the remote console through HP iLO.

The problem is that I am stuck to a screen resolution of 640x480.

(however, if I boot with the Ubuntu 16.04.1 ISO image and "Try Ubuntu", then I have a 1280x768 resolution)

Following the example of this manual: http://h10032.www1.hp.com/ctg/Manual/c04041473

I try to use a xorg configuration to fake the driver into thinking there is a CRT attached. I create the file /usr/share/X11/xorg.conf.d/xorg.conf as follows:

Section "Monitor"
  Identifier "Monitor0"
  # Do not remove the HorizSync or VertRefresh.
  HorizSync 30.0 - 110.0
  VertRefresh 50.0 - 150.0
  Option "DPMS"
EndSection

Section "Device"
  Identifier "Device0"
  Driver "nvidia"
  VendorName "NVIDIA Corporation"
  BusID "PCI:19:0:0"
  Option "ConnectedMonitor" "CRT"
  Option "UseEDID" "false"
  Option "AllowSHMPixmaps" "1"
EndSection

Section "Screen"
  Identifier "Screen0"
  Device "Device0"
  Monitor "Monitor0"
  DefaultDepth 24
  SubSection "Display"
    ### Put the largest resolution you support at the front of this list, and that will also become the default.
    ### For maximum flexibility, use "1920x1440" and rely on Resolution Matching.
    Modes "1920x1440"
    Depth 24
  EndSubSection
EndSection

and I reboot. but nothing changes. I am still stuck at 640x480.

I also tried using this http://xpra.org/xorg.conf, but then Ubuntu does not boot anymore (it gets stuck with the Ubuntu logo screen before the login screen).

So, how can I get a larger screen resolution using HP iLO remote console (without monitor plugged in)?