Can my son extend his 30-day entry stamp in Thailand due to medical reasons?

Hello. I live in Thailand, and my Son was at university overseas until a medical diagnosis meant he had to leave. It is a chronic disease which he undertakes specialist treatment for every 8 weeks, with frequent operations. Unfortunately, he was denied a medical visa as he was not inpatient, and as he is over 18, not classed as my dependent. We have therefore been flying him between in laws elsewhere in Asia and Thailand. This time, though, his next operation has been delayed and he is already in country on a 30 day entry stamp (not a tourist visa). His operation date will take him over the 30 day. Do we need to get him in and out again, or can he extend? We previously tried but were refused in Rayong, but other forums seem to suggest he should be able?

TIA and apologies for the long post.