Display a portion of the camera FOV

Hello !

Do you know if it is possible to display only a portion of the camera field of view ?
Using a RenderTexture with a second camera cannot be a solution in my case, mainly because the two cameras (if a second is necessary) have to share the same positions and FOVs.
Please note that the center of the camera is not in the center of the device's screen but slightly upward. This is the property that interests me.

Any ideas ?

Thanks !

 

Do you think this could be a solution ?

http://docs.unity3d.com/ScriptReference/Camera-projectionMatrix.html

I tested, this is really interesting !