I'm not sure which spices are safe for cats. However, there are various toppers I've seen mentioned that can help encourage a kitty to eat - crushed up freeze dried treats (chicken and shrimp seem popular), bonito flakes, nutritional yeast, parmesan cheese, tuna water . . . Personally, I use Fortiflora when Squeak is being fussy, but I saw on your other thread that your cat isn't too impressed by it.
Another trick you can try (if you haven't already) is heating up the food - I've had good success either heating the food for a few seconds in the microwave, or adding a bit of hot water.
Hopefully you have some luck getting Mr. M to eat!