For those who want to configure mouse wheel + back/forward buttons (I've been looking around the solution for 3 years...):

Section "InputDevice"
        Identifier      "Configured Mouse"
        Driver          "mouse"
        Option          "CorePointer"
        Option          "Device"      "/dev/input/mice"
        Option          "Protocol"    "ExplorerPS/2"
        Option          "ZAxisMapping"        "6 7"
        Option          "ButtonMapping"        "1 2 3 4 5"
        Option          "Emulate3Buttons"     "false"
EndSection