What type of data are you drawing on them? Do the internal nodes have their own displacements? Or do you just want to use color to display a scalar value?
MATLAB doesn't have a graphics primitive that matches the "serendipity element", so you're going to have to subdivide to something like triangles or linear quads. I showed the basic approach you'd use for this in this post on the graphics blog. It didn't include the basis matrix for this element, but I think that the 8 node serendipity is closely related to the quadratic hermite, which I did discuss in that post.
