There are much cheaper ways to do it if you look around, but anytime I do this the document is worth a heck of a lot more than the postage, so I just use FedEx: http://www.fedex.com/us/office/online-printing.html
To print the pdf, go to a business center in any 4 star hotel. You normally don't have to be a guest.
Do you live in one of those few countries on the planet that do not have regular mail service? Otherwise, why not use the local post office to send a certified letter containing your return? If you're overseas on April 15th you automatically get a two month extension. Even surface mail should make it to the US within 60 days.