Use the Distort Tool to define the handle by which you will stretch a path.

1.  Ensure that the path you want to work with is not selected.
   
2. Select the Distort Tool and define the starting and ending points for the part of the path that will be distorted. 
   
3. Set the midpoint of the part of the path that will be distorted.
4. To adjust the distortion, drag and rotate the handle. 
   
5.  After achieving the desired distortion, click Enter.