Post 12 in the thread linked below suggests GUWonder's strategy is a successful one:

http://www.flyertalk.com/forum/pract...l-citizen.html

The thread is some years old, I grant you, but the situation appears apposite to yours.

If at all possible, I would try to obtain an emergency travel document from the embassy/consulate beforehand. You can contact them for an emergency appointment if one is not available before you need to travel:
http://london.usembassy.gov/cons_new...ts/urgent.html