I don't have the book, but I have used the method of splitting the batting into thirds. It really helped! A lot! There are a few tricks. Once you are sure the batting is big enough (allow extra on all sides), I would work with the batting alone to cut into thirds.
Tip #1: Use a permanent marker (Sharpie works well) to mark the mid-point of each of the four sides of the batting. This will help you center the batting later.
Tip #2: I did a wavy cut -- large S shaped curves -- because it helps later on with getting the batting joined together exactly where it was split, plus it prevents any crease developing in the quilt in later years. Do both cuts. Do not move the pieces, but use the permanent marker to make lots of registration marks (just lines connecting the pieces) along the cuts. This makes it really easy later on to join the batting exactly as it started out.
Tip #3: Do not move the pieces UNTIL you have used a permanent marker to mark top and bottom of each piece. I also marked left/middle/right. This helps later on so when you add a piece the batting pieces are all the correct side up. It also saves a lot of time trying to figure out which piece is the correct one. Roll up the two end pieces to store.
Tip #4: Mark the mid-point of each side of the quilt backing and quilt top. This helps keep all the layers lined up.
Tip #5: I used basting spray, but it needs to be used very carefully to prevent a mess. I found it helpful to lay down paper or sheeting on each side of the middle piece of batting, a little underneath the batting, so I got spray only on the areas that needed to stick together. You do not want to get basting spray on any of the backing or top that is not going to be stuck to the current piece of batting. Or, you can pin.
Tip #6: I left about 6" along each edge unquilted. You need to leave the edges unquilted so you can attach the next piece of batting after the middle is quilted. Leaving enough space just makes it easier.
Tip #7: I rolled the excess backing and top together and pinned them so they stayed out of the way of my quilting.