easy rendering for Rhino in Windows
The Clay rendering is a combination of non-shadowing skylight combined with ambient occlusion. These are not ways the Flamingo NXT works.
To do the rendering you are showing in the thread, I would close off the tunnel ends. Then place a point light at the camera location. Turn on indirect light with multiple bounces. That will develop an clay-like rendering, but it may take a while. I think that is the best we can do.