Not sure about cats. I was worried about giving it to my dog the first time, too. For about the first 8 or 9 months I had her, she was extremely picky and wouldn't eat the same food more than 2 or 3 times in a row. I would almost have to "convince" her to eat. Then I FINALLY found the solution -- Nature's Variety raw frozen food. She is now a changed dog when it comes to eating. She will even eat other foods (stuff I cook) with gusto now.
I was afraid that if I added the Humaworm, she would start hating the raw food and then I would be stuck again. I crossed my fingers and hoped she would like it. She sniffed it at first and then ate it with just as much excitement. She even licks the bowl to make sure she gets all of the powder. Into about the 4th day of each round, I can tell she's starting to get to the point of maybe not liking it as much. Luckily, it is only a 5 day treatment.
Does your cat like canned tuna, canned chicken, or something like that? If so, you could try mixing it with that. The raw food I mentioned is good for both dogs and cats. My friend's cat wouldn't touch it, though, but her dog wouldn't either.