Can I apply for a visa extension in Thailand after my multiple entry tourist visa has expired?

Hi. I'm an American citizen staying in Bangkok with a 6-month MULTIPLE ENTRY TOURIST visa. My question about extending the M.E. visa is below....

(Sorry that this post is so long. I'm giving background information, hoping it will make my situation clear.)

I've been doing the 60-day visa runs. My original M.E. visa expired October 29. I went to Indonesia in September, re-entering Thailand on September 16. At that point, the Thai immigration officer gave me a stamp good through November 14 (60 days).

I took a trip to Myanmar, re-entering Thailand on November 11. At the airport, the immigration officer reminded me that my M.E. visa is expired, but gave me a stamp good for another 30 days -- through December 10.

I'm taking a trip to Japan at the end of the month and will re-enter Thailand on December 8. I am assuming that I won't get any kind of "automatic" extension stamp at the airport at that point. But I would like to stay a bit longer, maximize my time here before I have to go back to the states.

So once I'm back here on December 8, can I

apply in person at the Thai immigration office for (another) extension? Even though the officer at the airport already gave me an "extension" stamp? If I do apply, what is the maximum number of days I can apply for? Is it 30?

Thanks for reading this far.