It does NOT work, I promise
I killed a couple old P4's by doing this to them.
The die's nowadays don't need this anyway, they are EXTREMELY flat already and even if you removed the entire layer of non-conductive material you would not even get a 1* drop. I am addicted to lapping, and can vouch for the benefits of removing the IHS, but what you are suggesting really is suicide for your chip. And a pointless suicide at that.