We got an email from the US Consulate in Chiang Mai today telling us that immigration officials have been given a directive that gives them the authority to approve "extensions of stay for certain foreign nationals, including US citizens." I suppose that's what they do anyway, but it sounds like this means they have more latitude now. We're hoping this means you don't necessarily need a letter from your embassy, especially since A) you have to make an appointment to get one here in Chiang Mai and B) appointments are booked through March 31.