You can't make it on Gatorade, this has zero nutritional value. I would be checking with the GI doctors for solutions. It may be that he will have to have the tube relocated into his intestine, or they may have other options. Bottom line is that he cannot be allowed to continue losing weight. With three more weeks of treatment to go, and several weeks after treatmnet ends where he will still be unable to take things to any significant extent by mouth, he will be introuble if this continues.