Mini-Zun shares a script for Maya that brings to the Maya interface all the hidden and non exposed string options of Mental Ray 3.9 into the Render Settings window in Maya 2012. Check out the Maya Script for Integrating MentalRay 3.9 Features to The Maya 2012 interface here.

Mini-Zun writes on his script: “I know there are already script that enable string options (like Dorian’s one), but my goal was to do it exactly the same way as if autodesk had done it itself. Nothing to source, nothing to do, it’s here, just like if autodesk had done his job !
And I tried to respect syntax, naming convention and every thing else.
All new string options are added the same way they were before (declared in 3 global string array in mentalRayUi.mel) so they are created with the node miDefaultOption. New tabs, new layout, new controls, and everything I changed is done the way it was before.
I really felt like an archaeologist while trying to understand all mel file, looking in the folder /script/others for every procedure call and global variable usage to find where everything was natively created.”