Get an airfare with a flexible return ticket and book the initial return flight within 30 days should be the best thing to do. You can change it as you see fit later on. Alternatively, buy a single entry tourist visa. No need to present onward journey with a visa present.
It is exactly why I made this post: To let people know about this regulation. The most google-popular online resources do not mention this limitation at all. They just list immigration location and fees, but lack to refer to fineprint.
He does have that M version of a TR visa, but wants to stay 90 instead of 60 days. Without TM30 he will most likely not get any extension from what I understand.
It is certainly an inconvenience. Question is how he can file TM30 every day when living out of a tent. Hope he will find an officer who has symphaty with his travel style when he finally can apply for the extension. I think similar issues apply to people who want to stay on remote islands and or live on a boat.