Soft Edge on Z depth Mask--possible?

Hi
Using a Z Depth masking shader technique to ‘punch a hole’ through a mesh.
Unfortunately the edges are hard and the client would prefer them to be soft.

Doe s anyone know a way to accomplish this?

This is my simple shader applied to my masking object

Shader "Custom/InvisibleMask" {
   SubShader{
     // draw after all opaque objects (queue = 2001):
     Tags{ "Queue" = "Geometry+1" }
     Pass{
     Blend Zero One // keep the image behind it
   }
   }
}

Hi.
Have you found solution to that problem?

You may use dithering, it’s not true soft edge but in some cases may be acceptable.

If you’re using MSAA, you can use alpha to coverage, I.e.: AlphaToMask On. It works best in combination with dithering, because it is itself subpixel dithering.