I dont think you can get the your bass to eat pellets even if starving. Not your adult bass. In order for bass to become feed trained this is something that starts in the beginning stages of their life. I was able to feed train mine by stocking some in aquariums as fingerlings. And even then they all did not take to the feed. But I have quite a few bass in my pond that are feed trained. I can catch those with bread, pellets, dog food, etc. They bite and feed on everything that the bream bites and feed.

Your bass being underweight is because there is not enough food to go around or you have too many hiding places (Structure or plants and weeds) and they cant catch their prey. They are out of balance. You are going to have to remove bass. When I went through this I corrected it by removing only 12 bass. But my pond is only a 3rd acre. And looking back I wish I had removed only about 8 or 9. Hope this helps

3rd acre fertilized fed and aerated