Although there is no US partner, Spanair miles might be helpful since they are about to join *A some time in the next few months (I am not sure when). Depending on how many miles you earn in Argentina, you might be able to use a Spanair number on only a few UA flights later this year (if UA survives) until the Spanair account has enough in it for an award. This is obviously not ideal and has many possibilities for going wrong, but might be better than nothing.