If Adie is using NIV, technically a feeding tube can be placed in a RIG/PIG procedure. Some specialists will use the PEG procedure, but most shy away from doing it on folk with low FVC. There is a tube – MIC*G - which can be done just with a tummy full of air, not requiring an endoscope or, if these are deemed too risky, he can get a Nasal Gastric tube. NG tubes are usually for short term use but have been used successfully in longer term situations.
All risks v benefits need to be discussed with his team.

Best wishes to you both,