Good luck, my dogs LOVE cat food! ;D When I visit my parents house, the boys head straight for the laundry looking for the cats food before they even say hello to my flks My only solution would be as already suggested, keep it out of reach of the dog.
Our 20 month old loves cat food!!!! She will run to it if given the opportunity, we do our best to not make it available to her. If your cat is young, I agree with steltz02, put it up where the dog can't get to it. Our cat being 15 years old and not in the best of health is not able to jump up like that anymore, so we do what we can to keep the dogs out of her food. Life is never boring with V's around.
Back when we had our cat and two labs, we could never keep them out of her food. We ended up putting a chain lock on the door to the room where we fed the cat, (like you have on a front door) so that the cat could get in but the dogs could not. That stopped all cat food eating, except of course by the cat. She was older so she couldn't jump up on anything to get to it so we had to figure out a way to keep them away.
When I went to my breeder's house, his basement door had a tiny arch shaped cutout. It was big enough for the cat or for the adult Vizsla's head (he'd sit on the steps and peek through, too cute!). That would definitely be an option if you don't mind some modification to your doors.