It seems strange to me that anyone should care about having their honor code plagiarized (and in this case I'm not sure that the author(s) do care). If the point of an honor code is to get people to act better, shouldn't you be happy that your honor meme is spreading, even if you don't get credit for it?
In fact, to me, insisting on being credited seems to go against the spirit of creating an honor code.
I believe most honor codes have the prevention of cheating and plagiarism as their prime function -- which is why this is the perfect example of irony for your high school freshmen.
That said, you're addressing broader issues of intellectual property which certainly merit discussion. Giving credit, to me, is essential when basing work on a previous source.
In fact, to me, insisting on being credited seems to go against the spirit of creating an honor code.