A non-GIS solution may be in order.
Mixing GIS imagery with any number of available graphics and/or effects software may allow for more control of the appearance of the halo and, maybe, involve less time to get it just right, although at an increased cost for the additional resources.
I recommend investigating Adobe After Effects, or perhaps even Autodesk Maya. Lots of fun. TONS of learning curve. Perfect imagery.
Whats that old saying? Quality, price, speed...pick any two!
Not that helpful, I know. But it's good to know about the universe of computer graphics outside of GIS.
Gregory