Have you looked at using the Iray section plane node? It allows you to place the camera outside the wall and see through it for renders. If you turn on clip lights, it's as if the wall was there, and maintains reflections and the room lighting.
View attachment 2981474
As you can see the section plane is cutting the room in half, yet the wall and pictures are reflecting in the mirror.
The camera ignores the wall but any lights outside won't work, they'll need to be on the other side of the section plane.