Revit :: Cloud Rendering - White Background / Alpha Channel

I'm attempting to render a series of images in the cloud and my plan is to take these images into Photoshop so that I can apply a background from an image I possess.
 
To do this I need the background to be a plain white background, export as a TIFF or PNG, then add an alpha channel in Photoshop. The problem is that whatever settings I apply in Revit, the cloud rendering always gives me the standard grey / blue horizon background. I have changed the render settings using the render setup, through the view properties, through the graphic display, still no joy....