if you completed the selection process and got selected would you really take the year out. if not you can always say at the interview you would appreciate a quick decision because of GAP year and university places. if you find out you got accepted then cancel the year out and scrap university.
or you could say that you have a year out planned before university but if you were selected then you would return early from your GAP year and take up the position.
Another alterntive is to delay starting your time in the states until you hear from NATS.