Given you are UGS, I am almost 100% sure the DM list approach will work, especially if you mention it at check-in, and at the gate before the DM list is processed. Key for you will be to ensure the gate agent processes your seat change BEFORE clearing upgrades.
Make sure the GA is very aware of you...Last time i was in a middle(it was TED though) no one was aware or tried to get me a better seat. Me thinks you will fare better as long as they know you're around and your situation.