Treats! If he's food motivated, you want him to associate brushing with happiness, and treats=happiness in a lot of dogs' minds. After he comes happily with a wagging tail to be brushed for a treat every 20 seconds or so, start giving them to him every minute, then every 2, etc. The treats don't have to be big or anything. One of Liberty's favorites is chopped apples and carrots, or cut up dog treats so they're only teeny. It also sometimes helps to brush in sections, so you quit before they get too frustrated. Do one leg with treats, then 10 minutes later do another leg with treats, etc. Build up the time spent brushing depending on his reaction, until you can do all of him in one setting with him being cheerful, only giving a few treats here and there. I still give a treat after each leg, after each foot is shaved, etc.