The clever method Casa Sugar has devised is inspired by a traditional building technique called "wattle," which involves weaving together building materials in a lattice. To replicate the technique with the willow branches, you will need to hammer a series of narrow posts into the ground and then weave the flexible branches around the upright posts. Visit Casa Sugar for a helpful, detailed set of step-by-step instructions.
If you've got patience and are good with your hands, you could conceivably use this technique to build a larger willow structure, like an arbor, a fence, or even a tunnel. Arranging the anchor posts in different shapes could yield some interesting results. Has anyone tried this?