How to add noise to only the glow of a mask

This is a bit weird to explain, but I want to make a border for my stream overlay with a grainy glow that is looping around in a rounded rectangle. I used the Saber plugin to animate it, but the grain affects all the composition. I need it to ONLY affect the glow caused by the Saber, otherwise I would get random grain on my stream. How do I do this or is it possible to do it?

I don't know if you can see it, but the grain is in the black background. Also, now that I'm here, how would I go about exporting this video with alpha.