I know where to go to use the letter. What I'm asking for is to re-enable commenting on the post. This is still a developing and ongoing story, and sharing experiences (successes, failures, challenges) with other Americans is vital to the process.
USA seems in fact to be moving in the OPPOSITE direction, and now urging their citizens to get on a plane and return to USA, so I doubt we will see a USA letter anytime soon.
I have triple nationality myself actually, but it doesn't matter (I don't think?) because its all about the passport you used for entry. Example, I used USA passport to enter Thailand, so even a letter from the French consulate wouldn't do anything to get me another stamp in the USA passport...