Wasabi is working on a formal solution for working with Plex. The following forum thread describes a good method for doing this today:
https://forums.plex.tv/t/wasabi-s3-cloud-integration/237328
Note that this example uses Wasabi’s us-east-1 storage region. To use other Wasabi storage regions, use the appropriate Wasabi service URL as described in https://docs.wasabi.com/docs/what-are-the-service-urls-for-wasabi-s-different-storage-regions.