I went out with Mer and got a small eye dropper and a bottle of whole milk. That seems to have done the trick. The kitty ate 1 tablespoon of milk (bringing his total today to about 3 tablespoons, enough for a six-ounce kitten).

Then, Foley was attacking my hand while I was on my back, and so I took advantage of the situation to rub his tummy, with the (mostly) happy result that he peed all over my stomach. A happy day one so far!