I have a rather simple yet irritating problem. I want to have the common "semi-transparent ellipse reflection" on a path I created. The first thing that comes to mind is to just draw a white ellipse over the path and lover it's alpha. It works, but then I have nasty left over ellipse outside of my path. Here's a really straightforward example:

You see, I want the effect the ellipse has whilst laying over the black of my path, but you can still see the extra white that does not cover the path. I want this reflection ellipse to only cover the path and nothing outside of it. This is simple to do in raster design, but I want what I'm doing strictly vector.
So, in basic terms, how do I clip an object/path to an object path so it's almost a fill for it?
Thank you.