Did you ever figure this out? I have a similar problem - basically i want to do the exact same thing, but I don't necessarily want to add the values to a list-box. (i.e. populate drop-down options on-the-fly as the end-user enters in values for text fields).
so on PG.1 of the form, the user enters 4 different names, each in their own text field box (i.e. Person1, Person2, Person3, Person 4). On Pg.2 of the form, I have various drop-downs. I want to add the "Person" entries on Pg.1 to the list options in the drop-down fields on Pg.2