I haven't been able to find the answer by searching, perhaps because it can't be done. We can't seem to do a remote director because that apparently can't be done from a Windows machine. A Windows machine can be a client, but not a director, as far as I can tell.
So, we're looking at creating the backups on the server, then encrypting and storing that on the cloud. I've read about AWS Bacula, using the Amazon cloud services. Perhaps that is the way to go, but can the Amazon storage be set up as the director?
Okay, I contacted Bacula and they were very helpful. It is possible to have the director and client on the same server, and to upload the resulting backup to the cloud, using the Bacula S3 plugin for Amazon.