Embassy or consulate. I'll be visiting the US facility in Copenhagen on Thursday to get additional pages added to mine. Many will say that you have to mail it in or leave it for them to mail back to you but they can/will do the service while you wait if you ask nicely.

To the OP, once the passport is in the hands of the feds I'm not sure how easy it is for them to find it in the workflow, pull it out and expedite it. I know that there is an option when you submit it to pay for expedited service but it is too late for that now.