Graphics.Blit to RenderTexture. Impossible to produce a RenderTexture with alpha?

I have tried every combination of shader blending, texture formats, and ColorMask A..

I can not get a RenderTexture to have anything other than a purely solid alpha channel. Is this even possible?

Can a RenderTexture's alpha component be altered through Graphics.Blit?

 

Question still stands, but as I have done more experimenting, I should correct it.

I rewrote my shader as a vert/frag shader, and got alpha working! So the problem is in the surface shader workflow.

The question should now read:
Surface shader blitted to RenderTexture. Impossible to produce a RenderTexture with alpha using a surface shader?

 

I am using a vert frag shader and I am cannot get it to write to the alpha channel, how are you getting it to work?