Things like this are changing all the time, but for now you can hop to a second park and get additional FP once your original three are used up in the first park. (Unclear if you have to get the additional passes at a kiosk, or if you can use one of the online systems.) That's the way things are working this week - no promises that it will be the same next week!
I have tried booking more online and no luck. The kiosks at the parks for booking FB are crazy long. And they seem to move really slow as well, so I'm not about to try that. It's working out fine.