Multiseat on one video card

Question

I'm trying to set up a multiseat configuration on a single video card (Nvidia GTX 680) under Kubuntu 14.04. I can run two x-screens for one user, what nvidia-settings natively supports. So I think this should be possible.

Unfortunately my second screen stays black after booting but when I start another x-server in the second terminal it shows up at the second screen and the first one stays black.

Is there a way to show both at the same time?

My current settings are:

lightdm.conf:

[LightDM]
minimum-display-number=0
minimum-vt=7

[SeatDefaults]
xserver-command=X
allow-guest=false

[Seat:0]
xserver-command=X :0
xserver-config=xorg_seat0.conf

[Seat:1]
xserver-command=X :1 -sharevts
xserver-config=xorg_seat1.conf

xorg_seat0.conf:

Section "ServerLayout"
    Identifier "Layout0"
    Screen 0 "Screen0"
EndSection


# define monitors, devices and screens
Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "LG Electronics E2770"
    HorizSync       30.0 - 83.0
    VertRefresh     56.0 - 61.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 680"
    BusID          "PCI:1:0:0"
    Screen          0
    Option         "TripleBuffer" "True"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-1"
    Option         "metamodes" "HDMI-0: nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
    Depth       24
    EndSubSection
EndSection

xorg_seat1.conf:

Section "ServerLayout"
    Identifier "Layout1"
    Screen 1 "Screen1"
EndSection

# define monitors, devices and screens
Section "Monitor"
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "LG Electronics LG TV"
    HorizSync       28.0 - 83.0
    VertRefresh     58.0 - 63.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 680"
    BusID          "PCI:1:0:0"
    Screen          1
    Option         "TripleBuffer" "True"
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "metamodes" "DVI-I-0: nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
    Depth       24
    EndSubSection
EndSection