How can I make a node setup, where only round emitter glows outside the image? How can I make a light source glow and that only this glow surrounds the emitter?

I tried the following compositor setups:
In this setup the emitter (white) is blurred, so that it glows outside the image. But, what I don't want, the red piece is also blurred to outside the image


In this setup, the red piece is not blurred, but the glow of the emitter (white) doesn't glow outside the image either.


How can I make a setup, where the emitter glows outside the image, but red piece doesn't?
You could enable an emission pass in the render layers tab:



Then blur and overlay the Emit pass: