D5100 Focus Point Incidentally Changed all the time

The directional buttons for changing the AutoFocus point are located exactly where my thumb will rest on them when holding the camera. (please see image below)

This makes my thumb incidentally changing the focus point all the time.

Question: Is there any way to deactivate or lock the AF point changing buttons
at the back of the camera, as to avoid incidental changing AF point ?

(image source: dpreview)