You can now choose some arbitrary points by using the mouse, and fit a curve on the top of your chosen curve. It is simple and fun, and if you to use a different type of fitting technique, MATLAB has an excellent toolbox for this purpose.
Can be much better but it does what it says
As implemented, the function does not require the Curve Fitting Toolbox. The "required products" field should be corrected. I also think a couple of improvements could be made. First, the function should return the x and y coordinates of the clicked points. Second, you might consider plotting the fitted curve after sorting the x coordinates. Otherwise the line connecting the points can jump around if the clicked points don't have a monotonically increasing x coordinate.
Cute function ... it uses simple commands but does a nice job :)