Global Application Load Balancer in the host project to a Cloud RUN in the service project

[Mike-Seddi]

Google Released the Preview feature on July 11th 

Global external Application Load Balancers now support Shared VPC configurations where the load balancer's forwarding rule, target proxy, and URL map, can be created in a host or service project, while the backend services and backends can be distributed across multiple service projects in the Shared VPC environment. This is referred to as cross-project service referencing.

I'm trying it out so, I've create a host and service project and in the service project deployed the hello cloud run container.

No combination of configurations that I've tried allow me to have a Global Load balancer in the host project connect to a backend service in the service project. 

The error message

ERROR: (gcloud.beta.compute.url-maps.create) Could not fetch resource:

- Invalid value for field 'resource.defaultService': '.../beta/projects/mike-service/global/backendServices/bes-hello'. Cross-project references for this resource are not allowed.

Is it just not supported? or does someone have a example of this working?