Compress the file then print it out in easily OCR'able format (QR codes, perhaps), then physically carry it out of the country.
"You can't stop the signal, Mal."
STL files are nothing but sets of vertices - 3d points. The Zimmerman defense is easily applicable here. MY guess - the DoS is about to have their asses handed to them. Whether the files do fall under the purview of ITAR is irrelevant - with its current form, ITAR's restrictions on the dissemination of information are simply unconstitutional, and cannot be enforced as 3d design and printing technologies become so mainstream that people are building their own with little to no experience.