Tell docker client the location of private notary server?

How do you tell docker the location of a private notary server? My Notary config file specifies it, and it works when I use the notary client, but when I use the docker client it is looking for the notary server at the same IP address as the registry server.

Could you try specifying the DOCKER_CONTENT_TRUST_SERVER environment variable to point to the address of your notary server?