The Edge Expand uses another common technique for extending edges. This is done by unpremultiplying an image with an alpha and adding a blur. Also added to the gizmo is the option to use an animated transform node to generate a 2d vectorblur, which can act as a directional blur.
I have used this technique on a number of projects to help patch up flat areas and enhance edges after keying.
The creation was inspired by Johannes Masanz, a colleague at Automatik.
Download the nuke script from the link below