Hi there,
I was using this NodeGroups quite often with few setting adjustements, so i updated my old MaterialPass script.
Now it’s an fully feature addon, hopefully without any possible errors.
It generates material and layer(object) pass image in compositor, with colors from colorramp, so it can be easily modified by anyone later.
When you add new material just run it again, and it updates an old nodegroup (only one value is updated, but it is easier to have addon for it).
It also changes render layers alpha_treshold for minimum, but not zero (for example for people texture stilouettes).
Try and let me know here if it helped you.
materialPass addon: https://github.com/tibicen/blender-scripts/blob/master/materialPass.py
