I had fantastic luck booking a dinner for 16 at Citricos for my aunt's birthday. We will be dining there in about 10 days.
I had no luck with the regular dining line but they gave me the direct number to the Grand Floridan Cafe where I got "Pat." Pat seems to also handle the custom cake orders too. She's very busy but very good at her job. I wanted GF Cafe because it was more affordable but they had no availability, but she looked all over the resorts for me (Citricos, Narcoossee, etc.) and found that they could fit me in at Citricos. She said that they normally only take one large party per evening but since the large party that was already booked was coming in later in the dinner shift, if I could come in at 5:15 for dinner, they'd take us also. She ended up booking me four ADRs for four tables (total 16) that will all be sitting together in one area (I think they have a large group "alcove" too, but not sure if I'll be there.
Pat answered the phone right away when I called the GF Cafe line. She did not answer the other number right away for my custom cake order, but she did call me back within about 2 days. She does not work Sun and Mon, I believe so she can be reached Tuesday-Saturday.
Not sure what your budget is, but you can't beat the elegance of Citricos and the GF for a pre-wedding dinner.