No need, he will be allowed to exit Thailand, and come straight back for another 30 days stamp. He might need to pay a small fee, but they know full well he is most likely illegally working in Thailand, but they don't care, as said if they would, the Thai economy would collapse, that much is absolutely certain. It's the "illegal workers" from the countries that get a free visa exempt stamp (non mutual) that they are after, or as sglad said, the perputual tourists.
The 20K does not prove you are not working in Thailand but is being used as a reason to deny someone entry.
Someone that does not have multiple back to back tourist visas or entries on visa exempt, will not have to show the money, they will be allowed into the country no questions asked. The perpetual tourists are targetted, as they have been for quite a few years. The limit of two overland exempt stamps in a calendar year is targeting the exact same people. This is just step two.