So we held on to Buddha and scritched his chin and cheeks  so he could just watch Dasher and get used to him. By the end of it Buddha was not exactly chummy, but he was considerably less frantic. Later in the evening I risked putting Buddha on the floor and he restrained himself from making a wild charge either towards or away from Dasher, merely hunkered down and stared at him. And this morning, Buddha was actually relaxed enough (or hungry enough) to eat his breakfast, which is the first food of substance he's eaten since Saturday night.
Meanwhile, Dasher is getting cabin fever locked into the guestroom and I'm getting a bit concerned about that. He knocked over the lamp and cries when you close the door, and I don't want to keep torturing him just because Buddha is neurotic. I'm thinking that tonight we'll probably open the door and simply let the cats interact a bit. My prediction is that Dasher will be like, "Whee! I wanna explore!" and that Buddha will have a minor freak-out and go hide somewhere. But we've got to start normalizing relations between these guys, and sooner or later the door's gotta open.
Whether it stays open tonight, depends on how it goes, I guess.
 Cats have scent-glands in their cheeks that they use to mark territory, which is why you see them rubbing their face on stuff all the time. Scritching their cheeks expresses these glands and is very soothing to the cat -- it's one of the ways to put at a cat at ease fairly quickly.