I book the dates I want as soon as possible. Jet Blue seems to work on a similar system to
DCL. The cheapest seats go first. There are sales, but I have found that the flights I want are never included. I have never paid more than 79 per way from Buffalo. I do this by booking on the first day the schedule opens. If your flight $ goes down, Jetblue will give you a credit on same flight savings(eg. same flight you are booked on goes down.) I have only once had both directions of my trip on the same itinerary number.
Unless they hold off the next release, it does look like you might have to book two seperate itineraries, it will spread out the cost at least. They tend to open into only the first week of the month.
Penny