Hi, I can help out here, done S&S Using our flexticket and FFP and in USF, the holding areas are:
Finnegans bar where you can do the SS Houses early
Kidzone where you can do Parade/one of the sprung tent houses early
And the IOA Crossover:
Just before the park (USF) Opens for HHN, head into IOA, and go to Seuss Landing, there is a HHN Crossover there, then they let you in a side entrance, thus avoiding lots of queues and getting in a bit early too!
Hope this helps,
Kris