Reflection Matte:a head scratcher

[DP]

Ok, we have a scene which has balconies in front of windows, the balcony design is complex. We would like to reflect the balcony into the windows, which we can do easily. We prefer the max material with a vray map in the reflection slot to do this because we feel the behaviour of the glass looks more natural. Anyway, due to the final render size and the way max doesnt handle flat plane reflections well, its much more controlable to drop in pictures into the window panes as reflections. However we have a small problem, how how can we automate a mask around the reflections of the balconies in the windows?

We'd prefer not to set up another scene render using the max renderer, but at the moment thats looking like the only way. Anyone got any ideas?