Take every piece of advice you get on this board with a grain of salt. A few years ago I needed to add a person to my 'Ohana reservation. I tried the website and called the number, but the computer kept telling me no. I asked on here if folks thought they would help me at the podium. Everyone said "no way!" The feedback on here had me convinced that I was out of luck, so I fretted, and worried, and let it consume my mind. And what do you know? When I asked at the podium they were more than happy to add a person for me. It was no big deal.
I would for sure at least try walking up. It might work, and it might not. I would be prepared to stay on-site, but I might ask at the podium if there was some place you wanted to go.