Unfortunately, there’s nothing built in to CesiumJS to do that for textures. What this is doing is that the fragment shader on the globe discards pixels that are on the left of the split position. You can see this Globe shader here:
There’s no tutorial for doing exactly this, but I think to do it you’d need to create a custom material (as described here https://cesiumjs.org/tutorials/Geometry-and-Appearances/ ) and write your own shader to do that. If you’re unfamiliar with graphics shaders it might not be a trivial task.
The other trick you could do is render Cesium twice, once with the materials and once without, like in this example:
The easiest thing here if you just want to see it with and without material might be to create a button that when toggled will remove/add the materials.
Hope this helps!