Frame Overlay

Hi. Haven't played with FF in a long time and downloaded the demo to update my brush filter (create shapes for Photoshop brushes). Most are ok, but some get a little to square -draw to the edge which gives a straight edge or are too perfectly round. I want to generate and overlay something like this image



over each result just to be sure. The edges are 100% opacity, fading towards 0% towards the center. I want the frame to be a little ragged to destroy those few that are too perfect. Does anyone know of an example, or would consider a small snip to show how I might do this, and overlay it on say a perlin noise so I can see how to blend it with my filter?

Thanks.