I got to do ours on the roof of the Wilderness Lodge during Wishes, but the highlight of the night was watching the EWP from up there for Kari...
If you don't mind climbing up 3 flights and then down 10 flights, you could go to the roof of the contemp, we always go to the bay lake side of the roof top because it's less crowded. (take the fire exit stairs from the 12th floor, and stick something in the door to keep it from closing, or you have to walk down to the 4th floor, which isn't that bad).
If I was there, I would video tape it for you... our's however did not get video taped like it should have, so there's about a min in the beginning and about a min and a half after it all happened. I was so ticked when I watched the video. Thankfully I had two good photographer friends with me that took like 600 pictures.
If you do decide to do it at night, and get a photopass photographer involved, let them know ahead of time, so they can adjust the settings to capture it. I got caught off guard one night at the rose garden. Thankfully I was able to think fast and get some good ones in before it was all over. Either do it at the rose garden or liberty square bridge, you'll have a small crowd around to make it special, but no annoying faces in the background like you would at castle hub.
Good Luck... especially if you go to the contemp... my legs just about gave out getting to the roof of WL because I was so nervous.
Perfect idea, get two wine glasses from the aribas bro store, and get two single roses, cut the stems off and place them in the glass with the ring around each rose bud. Then go get yourself a good bottle of wine to share.