There will not, in fact, be ARCs of BLLB, as far as I know.
However, here is a possibility: travel to California, where I am now, on tour. Put on your favorite shirt and a pair of comfortable shoes. Examine my tour schedule to see where I (and my laptop) may possibly be at any given time. Analyze my Tumblr and Twitter feeds to see if I have left clues, being open to the possibility that I might be willfully misleading any possible readers who are doing exactly what you are doing. Apply to one of California’s excellent science schools. Graduate with a fancy degree. Invent a time travel machine. Travel to October 28th, get a copy of Blue Lily, Lily Blue from any available bookstore, and then travel to any date prior to October 28th.
Voila et voici.
The lack of arcs for BLLB is the saddest thing I’ve heard all day.