Automatically placing Catographic Polygon

Hi, I am very new to Cesium and am looking for some advice.

We already have an application set up to stream data into CesiumForUnreal.
What we want to do now is automatically clip specific areas on the map; these areas are set up in 3D software and exported with the scene (now they are represented by simple plane meshes).
I think I can read the tileset data in C++ and somehow get the mesh data, then generate Catographic Polygons based on that.
But the tiles only load when the camera is close enough, and they will be unload/reload frequently, so I am wondering if this is the best way to do it.
We are on CesiumForUnreal v2.16.1. What would be a better approach here?

What I can think of now is if we can stream JSON (like GeoJSON) into CesiumForUnreal, then generate Catographic Polygons using the point data. But CesiumForUnreal doesn’t seem to support GeoJSON?