Doorknob Effect

So I have to plan out and work on a shot for my Golden Doorknob film. We are doing a shot where a guy is looking out of a large glass window. We need to replace the background with an industrial city with smokestacks and such. We plan on overexposing the shot a little bit so that the light coming through the window is easy to luma key out. Then I'll probably put together a background by splicing different images together in photoshop. The thing im most concerned about is making the background look like it's outside and through glass. Whether that be by adding a reflection to the glass somehow or blurring the background and adding some other effects I don't know, so thats something i'll be playing around with.