A low-tech solution that doesn't require the machine to be opened up is to slide the sharp edge of a Stanley knife blade (just the blade without the handle) into the gap between the track-pad and the casing on the edge nearest the user; press down on the blade with your thumb; then role the top of the blade towards yourself. This slides the track-pad towards the back of the machine, after which it starts clicking again. It took a few gentle rolls to get the track-pad to move far enough. You might be able to achieve the same with a pry tool, but the blade has the advantage of being stronger at the tip, and having a broader surface area. I didn't find that this left any marks, because there is plenty of room to insert the blade without it touching anything along the sharpe edge.