Since they changed to the reservation system, you pretty much have to make a reservation to order your dessert if you want table service/full dessert menu. The walk-up window only has limited selection of desserts basically just scoops, and the Mini Mickey Sink, if you want any of their signature offerings like the Kitchen Sink or No Way Jose for example, you'll need to get table service.
We used to go to Beaches and Cream a lot before just for dessert. I think they expect it it's hard to eat a giant dessert and a lunch or dinner at the same time, and many guests are doing the exact same thing, no reason to feel out of place.
Last time I ordered the Grilled Cheese with soup, DH ordered a sundae. Waitress was super nice.