Non-functioning xorg.conf keyboard input option "XkbOptions" "compose:rwin"

[ineuw]

I am unable to assign the Rwin key to be the Superkey in xorg.conf but, pasting the following in the terminal works:
setxkbmap -model pc104 -layout us -option compose:rwin
Below is my xorg.conf file and the non working line is: Option "XkbOptions" "compose:rwin". Can someone please tell me what I am doing wrong?

Thanks.

# nvidia-settings: X configuration file generated by nvidia-settings NEW
# nvidia-settings: version 304.88 (buildd@roseapple) Tue Apr 9 12:24:47 UTC 2013

Section "ServerLayout"
Identifier "Layout0"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
Option "Xinerama" "0"
# The next four lines were added to the original and they work.
Option "BlankTime" "0"
Option "StandbyTime" "0"
Option "SuspendTime" "0"
Option "OffTime" "0"
EndSection

Section "Files"
EndSection

Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
# The next line was added to the original default and it doesn't work.
Option "XkbOptions" "compose:rwin"
EndSection

Section "Monitor"
# HorizSync source: edid, VertRefresh source: edid
Identifier "Monitor0"
VendorName "Unknown"
ModelName "LG Electronics LG TV"
HorizSync 31.0 - 82.0
VertRefresh 57.0 - 63.0
Option "DPMS"
EndSection

Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 210"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24
Option "Stereo" "0"
Option "metamodes" "1280x720 +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection