As you can see, it's not a staightforward task to implement this hybrid routing, but we found it worth it. We've now upgraded a large chunk of our apps to Angular and this was made possible by using Angular Upgrade and incrementally updating as we worked on various parts of the apps.
I hope this has been helpful. If you have any other tips or experiences please let me know. If you have any issues please raise an issue on the GitHub repo or feel free to submit a pull request.