Disable multitouch on some parts of a touchpad

The 4th gen Thinkpad Carbon X1 has no mouse buttons below the touchpad, but it is click-sensitive (a so-called *clickpad*). Clicking it on a small band at the bottom provides either a left- or a right-click depending on which side is clicked. (this click is a real mechanic clicking action, not a tap). My problem is that I am used to previous Thinkpad models, where there were physical mouse keys below the touchpad, so while mousing, I usually rest my thumb on the left key while using my index finger for navigating; then I can click without moving my thumb. However, on the new touchpad, as soon as my thumb rests on the touchpad, it counts as a touch on its own, and so the thumb and the index finger together become a multi-touch event, stopping the cursor from moving. How do I disable the multitouch detection for e.g. the lowest 1cm band of the touchpad, so that I can keep my thumb on it and not have it mistaken for a multi-touch gesture? Is there a way to track the other finger and discard the thumb until the physical click?