I got the filler blocks from Bibliostone. 4 1/2" strip of white & 2 1/2" strip of orange sewn together & cut into 6 1/2" squares. I do believe it is a great idea, as in my case to soften intense color, or to make your quilt bigger. I think Kass has done it too, but not sure what kind of block she uses.
I'll probably be last mailing mine. Everything is ready but 5 bags, I ran out of one extra fabric. My mind musta been calculating on a dead battery that day!
Love your fabric!