How can I make a part of a mesh to be invisible - ie: see through parts of walls...

I have a 3rd person camera that has it's .forward always pointing towards a specific object. Occasionally this object finds itself behind other objects/meshes (like walls for instance). I have a script that checks if this main object is visible by casting a ray from the cam's forward/center to this object's position. I would like to be able to make a "hole" in the any mesh hit by the ray that is not the main target object described above; I would like this hole to originate from the rayHit.point's position. I'm thinking the hole can only be an illusion, perhaps a superimposed alpha mask texture that will hide a circular subsection of the wall's alpha.... (like a square image, all transparent, with a black circle in its center). How can I do this in script? Apply an "layer mask" to a material...? Or perhaps another way of accomplishing what I am describing...? Thanks!