I was hoping you could add in Google Cloud Storage as a backup destination.
Note that this is different to Google Drive, as Cloud Storage is on the paid Google Cloud Platform, similar to Amazon S3 and Azure Storage (which I see you already have!)
I have set up my own *.bat script to upload there, but the problem with doing it this way is that the backup destination has to be set to a local disk location as well, which takes up space.
I've included the steps here so you can see it should be fairly easy to add
Uploading to Cloud Storage:
* create a GC VM, use a SQL Server Windows image. Under Service Account permissions, set Cloud Storage to "Read Write". Take note of the Service Account email address.
* create a GC Storage bucket, take note of the bucket name. Add the VM's service account email to the new bucket with Creator permission
* login to the VM, and from the command prompt you can now run:
gsutil -q cp database.bak gs://your-bucket-name/ to upload a file to the bucket