Despite what the mail help page says (see link) I don't see any way to add a name to the list from the ignore list page.

Far as I know, you'll have to wait until he makes a post to put him on ignore. I just gotta ask, if he's never contacted you and you can't find a post from him even when you go looking, do you really need him set on ignore? Is that going to make you feel safe? "I never want to have to read anything he writes." If he ever does make a post, you won't "have" to read it. Just saying.