Render through the objects
Alex Saplacan uses camera rays in a node setup to make objects transparent, while still having them render shadows etc.
A short cycles nod setup that helps you see through the parts of the mesh and keep their influence in the scene.
Ideal when you want to render through the walls of a building for example but you want that wall to contribute to the global illumination.
For a deeper explanation of his approach, read this article:
or you could just place that wall on a differ scene layer
Or you can just use clipping feature located on camera properties tab.