[Love the Magic]

Hi, just wanted someone to tell me if I can buy the HHN add on when I get to the park for that night? I hope to be there October 14th. My problem is I can't find exactly what I'm looking for, I want at least 4 day park to park pass with the add on but best I can get is a 3 day pass with add on. If I buy a 4 day pass I have to buy a HHN pass separately and it is much more expensive. I'm going with my wife and two teenage kids so 4 adult tickets. It seems I can buy a 14 day park to park pass in UK for very good price but the add on doesn't include the night I want to do HHN. But im led to believe that if I have any Universal ticket I can add on the HHN night I want when I get over to US. Can anybody confirm this? Thank you in advance.