AFAIK, palm sensing is not exposed through the graphical touchpad configuration tool. That said, you could try playing with it by using
To see what options are available, run
synclient -l | grep -i palm
PalmDetect = 0
PalmMinWidth = 10
PalmMinZ = 200
Those are the options I see, so, to activate the palm sensing, run
synclient PalmDetect=1, and then experiment with the values of the other two.
Minimum finger width at which touch is considered a palm. Prop‐
erty: "Synaptics Palm Dimensions"
Minimum finger pressure at which touch is considered a palm.
Property: "Synaptics Palm Dimensions"
When you find the right values, create a startup entry in Startup Applications with a command of the following form:
synclient PalmDetect=1 PalmMinWidth=xx PalmMinZ=yy
...where xx and yy are the desired values.