Intenta lo siguiente:
Section "InputDevice" Driver "mouse" Identifier "Mouse[1]" Option "ButtonNumber" "2" Option "Device" "/dev/mouse" Option "Name" "Autodetection" Option "Protocol" "imps/2" Option "Vendor" "Sysp" Option "ZAxisMapping" "4 5" EndSection
corta y pega Section "InputDevice" Driver "synaptics" Identifier "Mouse[1]" Option "AccelFactor" "0.0010" Option "BottomEdge" "4000" Option "ButtonNumber" "5" Option "Device" "/dev/mouse" Option "Edges" "1900 5400 1800 3900" Option "Finger" "25 30" Option "FingerHigh" "30" Option "FingerLow" "25" Option "InputFashion" "Mouse" Option "LeftEdge" "1900" Option "MaxSpeed" "0.18" Option "MaxTapMove" "220" Option "MaxTapTime" "180" Option "MinSpeed" "0.02" Option "Name" "Synaptics;Touchpad" Option "Protocol" "PS/2" Option "RightEdge" "5400" Option "SHMConfig" "on" Option "TopEdge" "1900" Option "VertScrollDelta" "100" Option "ZAxisMapping" "4 5" EndSection
Section "InputDevice" Driver "mouse" Identifier "Mouse[3]" Option "Device" "/dev/pointer1" Option "Name" "Autodetection" Option "Protocol" "imps/2" Option "Vendor" "Sysp" EndSection
Corta y pega Section "InputDevice" Driver "mouse" Identifier "Mouse[2]" Option "protocol" "IMPS/2" Option "Device" "/dev/psaux" Option "ZaxisMapping" "4 5" EndSection
Section "ServerLayout" Identifier "Layout[all]" InputDevice "Keyboard[0]" "CoreKeyboard" InputDevice "Mouse[1]" "CorePointer" InputDevice "Mouse[3]" "SendCoreEvents" Option "Clone" "off" Option "Xinerama" "off" Screen "Screen[0]" EndSection
Corta y pega InputDevice "Mouse[1]" "CorePointer" InputDevice "Mouse[2]" "SendCoreEvents" Espero que te sirva, tu diras