Thank you guys!
I was just searching PTC KB for a keyword and found a much better solution.
Set the Relation in your model to
MATERIAL=material_param("PTC_MATERIAL_DESCRIPTION")
and that will assign the description to the currently active material.
It is absolutely amazing that this was not pointed out earlier in my many tech support calls to PTC.
You can find the detailed solution at:
https://www.ptc.com/appserver/cs/view/solution.jsp?n=CS44055