First make sure the kennel is very warm and comfortable - think pillows and a hot water bottle. Whippets love warmth. You will have to not give in at all and it could take a week or more. But honestly,
Whippets, along with a lot of sighthounds are notorious for craving warmth and human comfort. Mine used to sleep not only on the bed but all the way under the blankets! And the fact that you already gave in once means he will whine all the longer tonight.