yes...you have to added this subsection on your /etc/X11/xorg.conf in the section screen:
add this subsection:
sudo gedit /etc/X11/xorg.conf
Virtual 2304 1600
my virtual is 2304 1600 because one of my monitor is 1280x800 and the external is 1024x800.
then close the file and reboot and type this in console
and then reboot again,connect cable and type in console:
sudo update-initramfs -u
xrandr --output VGA --auto --right-of LVDS
xrandr --output VGA --off
on my mac works well. if you wanna you can get the grandr from synaptic. is a gui application that you can use after changed xorg.conf file.