How can I set up two-finger scrolling on an ALPS touchpad that doesn't support multiple fingers?

The relevant output from `xinput list`

is as follows:

⎡ Virtual core pointer id=2 [master pointer (3)] ⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)] ⎜ ↳ PS/2 Mouse id=12 [slave pointer (2)] ⎜ ↳ AlpsPS/2 ALPS GlidePoint id=13 [slave pointer (2)]

and the output of `synclient -l`

is:

Parameter settings: LeftEdge = 153 RightEdge = 870 TopEdge = 115 BottomEdge = 652 FingerLow = 12 FingerHigh = 14 FingerPress = 127 MaxTapTime = 180 MaxTapMove = 56 MaxDoubleTapTime = 180 SingleTapTimeout = 180 ClickTime = 100 FastTaps = 0 EmulateMidButtonTime = 75 EmulateTwoFingerMinZ = 139 EmulateTwoFingerMinW = 7 VertScrollDelta = 25 HorizScrollDelta = 25 VertEdgeScroll = 1 HorizEdgeScroll = 0 CornerCoasting = 0 VertTwoFingerScroll = 0 HorizTwoFingerScroll = 0 MinSpeed = 1 MaxSpeed = 1.75 AccelFactor = 0.156495 TrackstickSpeed = 40 EdgeMotionMinZ = 14 EdgeMotionMaxZ = 79 EdgeMotionMinSpeed = 1 EdgeMotionMaxSpeed = 102 EdgeMotionUseAlways = 0 TouchpadOff = 1 LockedDrags = 0 LockedDragTimeout = 5000 RTCornerButton = 2 RBCornerButton = 3 LTCornerButton = 0 LBCornerButton = 0 TapButton1 = 1 TapButton2 = 3 TapButton3 = 2 ClickFinger1 = 1 ClickFinger2 = 1 ClickFinger3 = 1 CircularScrolling = 0 CircScrollDelta = 0.1 CircScrollTrigger = 0 CircularPad = 0 PalmDetect = 0 PalmMinWidth = 10 PalmMinZ = 99 CoastingSpeed = 20 CoastingFriction = 50 PressureMotionMinZ = 14 PressureMotionMaxZ = 79 PressureMotionMinFactor = 1 PressureMotionMaxFactor = 1 ResolutionDetect = 1 GrabEventDevice = 1 TapAndDragGesture = 1 AreaLeftEdge = 0 AreaRightEdge = 0 AreaTopEdge = 0 AreaBottomEdge = 0