I had the same problem once at the Harrisburg, PA airport when I forgot to check my Swiss Army Knife when deploying to Haiti after the 2010 earthquake.
A helpful police officer at the TSA checkpoint asked me for $5, went to the nearest airport shop, bought me a mailer, and on the spot I dropped my knife into the mailbox. It was home when I arrived back home.
Makes me wonder if being really prepared is keeping a stamped padded mailing envelope in our carry-ons at all times is what being really prepared requires.
8^)