I've made my own geometry and copied the shaders of the PerInstanceFlatColorAppearanceFS.glsl to use in my own appearance. My library can be found here... https://github.com/brianolsen87/cesium-plugins with examples.
One issue I'm working out now is that I'm having trouble integrating a worker in this "plug-in" set up I have (Therefore I can't generate the triangles asynchronously). I have an open question posted here...
about it.