Rotating an Ellipsoid in Cesium


I'm attempting to visualize the 1-sigma 3D covariance matrix for a spacecrafts' position in Cesium. I believe the appropriate way to do this is by using an ellipsoid object, which takes as its arguments the x, y, and z ellipsoid axis parameters. I have properly sized ellipsoid objects displaying, but now I need to rotate them in order to orient them correctly. I have a rotation matrix/quaternion to perform the rotation each ellipsoid I want to render, but I can't figure out how to rotate an ellipsoid objects.

So, my questions are: Is it possible to rotate an ellipsoid in Cesium using a rotation matrix/quaternion? If so, how is this done? If not, is there another way to properly visualize a covariance ellipsoid in Cesium?