I've seen this brilliant construction once: the keyboard PCB was mounted to the chassis with a piezo element in between. The harder you pushed the buttons, the harder you pushed the piezo, and hence things (in this case scrolling through the display) would speed up.
In your case, you only need 2 levels, maybe a comparator after the piezo would even eliminate the need for an a/d.
A level click could also be generated electronically.