You cannot buy travel in pesos without being a resident. Any travel purchases for foreigners must be done on a foreign credit card or with USD at the official rate. I am not sure there is anyway to get around this anymore, unless a local bought them for you, but you'd have to use a fake DNI number.
People used to report buying resident tickets, checking in online and then going directly to the gate without checking bags as a way to get around any DNI check. Doesn't seem worth the risk to me.
Last edited by mccomb; Jan 16, 2015 at 2:17 pm