We asked back when we visited in May, there is no way to get the Southwest discount ahead of time, only at the gate. You may want to consider what the "cost" of your time waiting in line is and then decide whether to purchase tickets in advance and get a 10% discount, or get 20% and have to wait for a while in line to get the tickets. Its a toss-up in my book, but if you think its going to be VERY crowded, I'd just buy in advance and be happy with the 10% I'm getting.