I have to be honest – texturing, shading, and rendering are not strengths of mine. If my renders look good at all, it’s either thanks to a miracle, or readily available (and free) documentation found online. 
So anyway, first up is the ctrlBuffers utility by “Francescaluce”. If you haven’t checked it out already, MUCH more information can be found here. There are 3 parts to this shader – Store, Write, and API, and each one needs to be used for it to work (as far as I know).
The buffer_Store node is probably the easiest of the three to set up -
Connect your shaders to the appropriate buffers, name them (just to keep things organized), and don’t forget to click the ‘store’ attributes. If you have a ‘Beauty pass’ shader, you can plug it into the render.buffer.
Next is the API node, which basically tells the render that there are buffers to be rendered. I think.
Create any basic object, and apply the buffer_api node as a Geometry Shader -
Options are fairly simple, you really just to have let it know how many buffers are going to be rendered -
You shouldn’t have to worry about the object after this, the api node should make it non-renderable.
That just leaves the buffer_Write node. Select the camera you intend to use, and create an Output Pass under the Mental Ray rollout -
Under the Pass Options, the buffer_Write node will be used as the Output Shader.
For the most part, the Buffer Write options are fairly straight-forward:
type in the output path for your images, the format, buffer names, etc. -
That’s about it. The only other thing I can think of, is that although you might create a buffer_Store node for every object in your scene, you’ll only need one Write and API node.