mezuzah question

A co-worker friend of mine came into my office with a very interesting question that I did not know how to answer. He asked if 1) it would be offensive or 2) just plain wrong of him as a non-Jew to post a mezuzah on his new home that he and his wife are building.
I honestly don't know how to answer this. I told him I would ask some sources and get back to him. So here I am asking.
After thinking a brief moment, I came up with this PC answer, hoping that it appeases him in this world of non-Jews where I am an outsider and a minority...the only one on my floor and in my entire company as far as I know.
I told him that if it was important enough for him to ask about it and to be considerate in the thoughts of others, then it must be meaningful for him in some way and that I would think that he should hang it up. Of course, he most likely won't have a a sofer write the thing or a minyan present when he hangs it or a rabbi to check it occasionally, so the religious significance is much less in any case. But he will feel peace at having it on his home (and some other quote on his back door) and not having a regret at not having that extra added protection in this world.
I still intend to personally question a few rebbitzens but I think he would never invite me over so it for sure wouldn't offend me,
He is also consulting with an "observant" friend of his, Brian, who lives elsewhere than the great state of Texas and I encouraged that as well.