sounds like a funny trip just for opening a bank account, ha ha.
here on bank caribe and on banco bhd they also ask for letter of reference and police conduct papers when you are not a resident with up to date cedula.
stick with the La Nacional where you opened the pesos account, show up some nice account movements in and out and as a known customer they will make it easy to give you a additonal account, this time in US$ after a while.
in case of the banks it is always very helpful to stick with the smaller offices where you know the person in charge in person, they can move a lot, because they can 'recommend' you to their main-office as a customer or not.
it is the same when you request a credit, huge differences from one spot to an other, and to be known in person helps more than a lot.
Mike