Keying out a background with glow

Hi There,

Using premiere pro, it is possible to key out a blackbackground from a video. However in the attached short video I would like to keep the blue neon rotating ring together with the blue haze that surrounds it and key out the black background although I do not want quite as much of the haze to be present once the background is keyed out.  

Using the image below. I would like the areas beyond the outer ring I have drawn to be completely transparent. ( A + B).  and the central area to also be completelty transparent so that  the limit of the glow would be with in the area shown by the green arrow.

I hope this makes sense.

In a nutshell I want to key out but maintain the gradient glow from blue to black (transparent when the black is keyed out)

Thanks in advance for help.

Rob