Comment 3 for bug 851362

I patch lightdm sources. This is actually a workaround and NOT a proper solution.
Apply the attached patch and put in your lightdm.conf something similar to

[Seat:0]
type=xlocal
xserver-display=0
xserver-command=/usr/bin/X0
xserver-layout=Seat-0
xserver-config=/etc/X11/xorg.conf
user-session=openbox

[Seat:1]
type=xlocal
xserver-display=1
xserver-command=/usr/bin/X1 -novtswitch -sharevts
xserver-layout=Seat-1
xserver-config=/etc/X11/xorg.conf
user-session=openbox

PS: i patch only xlocal seat configuration. if you need a VNC, you'll need similar patch for seat-xvnc.c, xserver-xvnc.c and xserver-xvnc.h files.