When will it be? What about Tabard Inn? That's walkable, but you may not be able to get a res depending on how soon it is. You could also walk to Restaurant Nora. Other suggestions (don't know how quiet/romantic/not casual you want so I'm just throwing things out here):
Restaurant Nora
Pesce
Hank's Oyster Bar
Bistrot du Coin
Go to Open Table and you can search for restaurants in the Dupont area and their table availability. I wouldn't do room service (unless there's something about that that really appeals to you

). Go out!