How to integrate ES6 library without compiling the source?

[Punji]

I have a React application based on create-react-app which already uses OpenLayers (ol project v5.2.0). Now I need to integrate Cesium into it. I don't want to eject my application, so the webpack configuration is not accessible to me. In other words, I can't compile the ol-cesium ES6 library source as part of my project.

I tried to import ol-cesium v.2.2.2 from "dist/olcesium.js" but I got an error:
-> ReferenceError: ol is not defined.

Is there any way to integrate Cesium into my project? Why ol-cesium project does not have a proper distribution like many other npm modules?