Potential demand for Bitcoin in these countries could be companies that buy from the US and receive a discount for paying with Bitcoin. An intermediary buys Bitcoin for the receiver of remittances and sells to those companies.
That could work. Some guy with a shop in Mexico selling say used iphones could provide a cash sevice giving people pesos in exchange for payment in bitcoin and then use the bitcoins to purchase iphones from the US. Assuming there are sellers in the US who will ship goods to Mexico for bitcoin.
Edit: please leave a comment when downvoting