You can use dynamic binding to bind each list box to data from your data file (you may have already done that, from what you wrote).
But I'm not sure how you can "share" that same binding across all fields, so that each dropdown doesn't need to bind separately to the (same) data. You can't just set each dropdown to "global" binding, because that will make the value of the dropdown global, not the items. I'll look into how to do what you want.
One possibility would be to "lazy-load" each dropdown only when it's used; write some script on the Enter even to populate it. Maybe bind some hidden list to the data you have, and then use script in each visible dropdown to populate it using the same items in your stored list, but only populate it on Enter? And, check if it's already populated (on enter) so you don't do it again if it's not needed.
Mike