I'm still waiting for the pre-order deal to appear on Kobo and Barnes & Noble. Will update with a post here and on Facebook when it does.
Here's what I suggest - if you do a search on Amazon for "Voices of Blaze", nothing useful will come up. But if you scroll to the bottom, there's a box that says: "Search Feedback: Did you find what you were looking for?"
Tell them "No," and then fill in the box, telling them about how amazing The Fireblade Array is (:-)) and that they really ought to carry a pre-order of Vol 5 just like the other bookstores. If enough people do this, we might gain enough traction for Amazon to let me list the book early and offer the same deal to all my readers.
I think it's worth a try, if nothing else. Amazon does like to please its customers to keep you all coming back!