We have a couple different layers we can work with here, both on the computers and the network.

He asked for a specific thing, and you answered with nothing at all.

That's OK, I figured he or she may not want to publicly reveal details, that is understandable in this case imho. As I said I was just curious if it was maybe a simple solution that could be implemented elsewhere.

He also indicated he understood that one might not want to detail their network security measures in detail. ;)

What if GP was working for Grammarly and wanted to avoid detection?

I do not, but that's not an invalid concern.