A quote from Roaring Silence at the beginning of chapter 3 — page 47 in the Kindle edition:
Imagination relies on empty perception. Painting relies on empty planes. Sculpture relies on empty space. Music relies on empty time. Literature relies on empty concepts. If we are to realize the art of freedom, if we are to discover our creative potential, we need to rely on the experience of our intrinsic vibrant emptiness—the beginningless ground of what we are.
This one doesn't stand so well on its own as some of the other quotes I've looked at. It relies on the context of the rest of the book, I think. But I've been remembering a quote about literature as "conjuring with empty concept." This is so close I think it must be where I got the phrase. It doesn't use the word conjuring—it says relies on.
I think I confabulated the partial quote in my head, and I was thinking of this one. Conjuring with empty concept could imply there is such a thing as nonempty concept, which would be silly to imply. The phrase "relies on empty concepts" doesn't imply that there is any such thing as nonempty concepts.