Thanks much to everyone for all the support and suggestions.
The patient is eating better today than yesterday, but still not quite what he usually does, so tonight was more tummy massage and some syringed pineapple juice and baby food. He doesn't appear to be in pain or discomfort; no tooth-grinding, posture is relaxed, he was even flopped and napping at one point. The tummy massage is definitely helping things along, he tends to eat more afterwards. He ate some more parsley, but turned up his nose at the dish of papaya in pineapple juice I put in his cage. I used to give that to him every day as a hairball preventative, and it worked great until one day he flat-out refused to eat it and that was it. I just put some romaine in his greens dish and he went to town on that, and I'll be letting him out for more exercise soon to help keep things moving.
My vet's office is open until noon tomorrow, so that may be an option depending on what he's doing for poop tonight and in the morning. What he's been pooping has been small, dry and hard; it's possible that's just because he's not getting as much fiber as he normally does, but I'm still a little concerned that there could be more blockage in there than expected. One more night will give me a better idea.