Thank you for all your suggestions and comments! Last night I went to PetSmart and picked up a couple of cat toys and a dog toy that was a small ball made out of rubber and had a rubber-band feel. Gave it to the cat last night -- and he could care less, LOL!
But I also got a few lightweight plastic bobbing-type things - like milk-neck rings, and some that looked like curled ribbon. We'll see if those catch on.
As I said, this cat is not usually playful. He has some fake mice, which he ignores. (Can't compare to the Real Thing, which he catches daily in the summertime and leaves as presents!)The one thing I've seen him really enjoy is a plastic pen on the floor - but even that doesn't occupy him long.
Sue