I don't know if it will be possible to do this but it seemed worth a try because there was only one date out of a whole week in which we could get the upgrades. Similarly, if I follow Viajero's suggestion of starting a LONE4 from EZE instead of SCL, I'll first try to reserve a stand alone ticket for EZE-JFK-EZE and hope that will carry over.
By the way, trying to do all this by Skype is not working from here (Patagonia) the way that Gardyloo had described (in a separate thread). The connections are terrible and you can be on the line almost completing an itinerary and then the call drops out and you try to start all over again.