What do you mean with ignoring? That is more or less what it should do already. If a page returns 404 or 403 it should display that the page could not be added but still add all other ones. What happens for you and what would you expect to happen?
Thanks for your help!
Perhaps the server isn't returning the proper status code (I didn't check), but I have seen plenty of pages come up with just a page not found or a 403 message.