Pen tool Scaling (Silverlight, Expression Blend)

I have a custom shape which is drawn out by the pen tool. For example, lets pretend I drew a trapezoid. When you scale the object, the whole thing gets resized app开发者_如何学JAVAropriately.

My question is: When I scale it width-wise, I only want the top and the bottom edges to expand. I do not want the 'diagonal' edges to be changed. What is the easiest way to go about doing this?

Right-click the Path in Objects and Timeline and select Group Into -> Grid. Then pick the Path again and change its HorizontalAlignment to Center. Now resizing the width of the Grid will not distort the Path.