1) Directly attach the monitors to get the EDID
2) Install monitor-edid (CentOS)

yum install monitor-edid

monitor-get-edid  > /etc/X11/eeid1.bin

3) Assuming monitors are the identical do it again for the second monitor (otherwise swap them over I suppose

monitor-get-edid  > /etc/X11/eeid2.bin

Use the following xorg.conf

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 319.23  (buildmeister@swio-display-x86-rhel47-11)  Thu May 16 20:17:05 PDT 2013


Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
    FontPath        "/usr/share/fonts/default/Type1"
EndSection

Section "InputDevice"

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

Section "InputDevice"

    # generated from data in "/etc/sysconfig/keyboard"
    Identifier     "Keyboard0"
    Driver         "keyboard"
    Option         "XkbLayout" "gb"
    Option         "XkbModel" "pc105"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "CRT-0"
    HorizSync       30.0 - 83.0
    VertRefresh     50.0 - 75.0
    ModeLine       "1280x1024" 108.00 1280 1328 1440 1688 1024 1025 1028 1066 -hsync -vsync
    Option         "CustomEDID" "CRT-0:/X11/etc/edid1.bin"
    Option         "IgnoreEDID" "false"
    Option         "UseEDID" "true"  
   EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "CRT-1"
    HorizSync       30.0 - 83.0
    VertRefresh     50.0 - 75.0
    ModeLine       "1280x1024" 108.00 1280 1328 1440 1688 1024 1025 1028 1066 -hsync -vsync
    Option         "CustomEDID" "CRT-1:/etc/X11/edid2.bin"
    Option         "IgnoreEDID" "false"
    Option         "UseEDID" "true"  
EndSection


Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "Quadro NVS 290"
    Option         "UseEDID" "False"
    Option         "ModeValidation" "NoVertRefreshCheck"
    Option         "CustomEDID" "CRT-0:/X11/etc/edid1.bin; CRT-1:/etc/X11/edid2.bin"
    Option         "IgnoreEDID" "false"
    Option         "UseEDID" "true"  
    Option         "ConnectedMonitor" "CRT-0,CRT-1"
EndSection

Section "Screen"

# Removed Option "metamodes" "CRT: nvidia-auto-select +0+0, DFP: 1280x1024 +1280+0"
# Removed Option "metamodes" "CRT-0: 1280x1024 +0+0"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "CRT-0"
    Option         "metamodes" "CRT-0: 1280x1024 +0+0, CRT-1: 1280x1024 +1280+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection