Writing to UAVs from pixel shader without using OnRenderImage

Trying my luck with the forums here. Didn't get much views on the q/a page.

Please see
http://answers.unity3d.com/questions/895529/writing-to-rwtexture3d-using-a-pixel-shader-withou.html
for details.

I believe Unity doesn't bind UAVs when using them in a pixel shader from OnPostRender. It only works, like in Aras's DX11 example, from OnRenderImage with Graphics.Blit.