Yes, you can. I already have one person on ignore. (Who? It'd be rude to say who, so I won't.)
See, up near the top right, "user cp" button? Click on that. Then you'll see "Edit Ignore List." Click on that. Then you can put in their user name, update the list, and BOOM, you're done.
Just so you know, once they're on ignore, you can't see what they said, even if you click on the "This person is on your ignore list, click here to read their message" link. (Or maybe my "anti-ads" software is just blocking the link?)