That is weird...because I spoke with a cast member on the phone yesterday that said you could book the additional fastpasses from your phone. He told me that if you have 3 booked, and use 1, that you can then book another immediately and it could be for any park. He said he just did this 2 weeks ago.
Of course this contradicts what I have read here. I hate when they tell you things that don't seem to be true.
I am going with my teen aged daughter in March and have never used the new fast pass system so was asking a few questions.