I was going to say edge blend also :)

I don't know if you are trying to avoid post work for the challenge or to keep the process simple...  But if you want the aura to extend beyond the filter, I have created a few filter setups for virtualdub to do bloom.

The idea is that you need to keep the aura brighter that anything else in the scene (or those things will glow also).  First you load the image in and crank the contrast up until only your aura remains visible against a black background.  It appears I used the threshold filter to do this.  Then you apply a gaussian blur, and use filterblender to add the aura to the original image.

Attached is the setup of one that worked well for putting an aura around an overhead lightglobe.  Not sure if that one adds chroma or just luma, but it shows how the process works.