To use the built in address field. You would have to modify the view-functions.php file, function display_address($element), to either only show the two countries or to do a select case to only show the two countries based on the form.
However, from looking at this real quick it does not seem like the form information is available. It looks like the function only knows the element and not what form it is attached to so I am not sure you can do the select case.
It would probably be easier to build you own address block using the standard components.