Isolate Bloom inside a mask in postprocess

Hi!

I’am trying to only have the bloom effect inside a circle in a postprocess.
I have tried with materials and fiddling with both the scenetexture Postprocess inputs and the blendable location with no good results.

Even tried to fake it with blur but no luck with that either!

Think of it like you only want bloom in a sniper scoope not outside of the scoop.

Any hints, please!

Photoshoped image of desired result.