I haven't personally had to do this, but there is a video on YouTube by Brian from Touring plans called "Riding Flight of Passage with No wait" that may help. From the research I have done for my own trip this year (if I cannot get FP+), it seems like one of the best strategies is to get to the park quite early so you can be one of the first people queued up at the turnstiles and will be able to be one of the first groups to FoP when you are let into the park. After that since most people are wanting to ride FoP, the wait for Na'vi is still pretty short after you ride FoP. I have also read where some people are having luck jumping into line close to the park close with little waits (30-45 min).