I'm sending out paper RSVP's that don't have clear instructions for any plus ones. Most everyone is traveling a few thousand miles for this. We have added all wives, husbands, boyfriends, girlfriends, SO's, but we still want people to know they can have a plus one. We added the guest list to our knot website and want to add the option for people to put a plus one if they chose to RSVP through the website. How do you do this?