Hi keera,
Perhaps you can ask your doctor about inserting a PEG tube (feeding tube inserted directly into stomach). The idea of it is more difficult than the actual use of it. Eric had one from the beginning of treatment but didn't use it until about the third week. It has been a lifesaver..and yes, you can maintain and gain weight from strictly ingesting Ensure! It also helps with keeping him hydrated which is essential for healing.
Keep encouraging him to swallow, even if just a mouthful of applesauce or sips of water each day to keep his "swallowing memory" intact. Good luck!