How can a blur material be used for 3d objects with opacity masking?

Specifically, I am trying to create a blur material that is masked to certain areas of the face mesh (like around the lips, and under eyes).

I'm not too familiar with using graphing nodes like the material editor but it seems the opacity layer of the default gaussian blur/smoothing materials are UV mapped to the screen. I'm thinking that they have to be UV mapped to a 3d texture sample..? Any guidance is appreciated.