Use an invisible light behind the camera (like a Light portal in 3ds Max or one of ArchiCAD's general lights (rectangular) set to light blue to match a sky) and place it out of view behind the camera.
Also you can turn up exposure some more and then also turn up Highlight suppress (compress?) value to reduce the window getting blown out with light from outside.
You could also try to change the camera system to photographic exposure instead of simple exposure (or the other way around) to get more range.
Worst case scenario, just add more lights inside your room.
That's how it would be built i real life anyway
