Hasta La Motion!

I have an animated camera flying backwards over a city, then backwards through a window. Now, the z value of the card I used for the window (I used a noise node to create dusty glass) logically covers the city cards and cubes behind, therefor destroying my zblur. Is there a way to exclude only the window card from the depth channel without having to render out two scenes, one for depth with the card disabled and one with the card turned on? maybe it’s a silly question, but on the other hand I could have overlooked one function