I'm under the impression that the stroke has no "end" as such, since it's merely a stroke created by 3D Stroke, and relies on the mask or path for its' beginning and end. Maybe you need to pick whip the ends of the path to get it to work.
Otherwise, the Beam effect is commonly used for this, since it actually has points at the beginning and end, which can be accessed in Expressions.
There's another really nice, inexpensive script called LinesCreator:
http://linescreator.com/
This will do most of the heavy lifting for you, short of the rubber band effect, which can be done with keyframes, or using the second link I gave you above.
Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com