Querying occlusion system?

I want to override IsNetRelevantFor so that objects you don’t see aren’t updated. How do I ask, for a given actor, if he can see another actor? A linecast won’t work because you might see the corner of an object but not it’s center. It also won’t work if you can see it through trees (because the linecast treats transparent meshes as solid).

Actually for this to work the camera would need to be at the actor location, so that’s no good.