Vray Environment fog as a render element?

[CEJ1976]

Hi,

 

Does anyone know how I would render the environment fog (trying to simulate sun light coming through a window) as a render element?

 

Currently i render it by applying a black material to all geometry in the scene and then turning on the vray environment fog and overlaying this a screen layer pass in After effects.

 

Has anyone got a more productive method?

 

thanks.