We had a slightly different situation - we were bringing family members as a treat, and we were paying for their dining plan. So we didn't want to pay for the dining plan when they checked in, seemed kinda tacky.
We were able to fax in our payment (via Credit Card) to SSR the morning of our arrival. I think they said fax it in after 6 am, or something like that. Member Services set it up for us, and I called SSR to verify. Worked fine, when we arrived, they had all 3 rooms pre-checked in and all the room keys were ready.