Plug-in Menu location:
Run plug-in, specify center-x and center-y to expand from, and chose scale down times (2 works best for me I think).
After it's done you'll have to do Image/Fit Canvas to layers to expand the canvas to see the rest of the new layer.
The new layer is larger in order to fit the expanded shape (it's a total hack and I wasn't sure of actual size so I just made it bigger to allow more room to work with, feel free to crop it down to your liking).
See also: High-resolution of the below altered Calgary Flames logo which can be used as a facebook frame for your fb profile image(s).