There is currently no declarative way to have addMesh called on your behalf, but you can do so by capturing the references:

useEffect(() => {
  if (highlightLayerEL.current && sphereRef.current) {
    highlightLayerEL.current.addMesh(sphereRef.current, Color3.Green())
  }
}, [sphereRef, highlightLayerEL])
Preview
Typescript
Javascript