In 3.7.3. Connect APIcast from Other Deployments the documentation states:

If are using the Docker containerized environment: docker run -e BACKEND_ENDPOINT_OVERRIDE=https://backend.<your_openshift_subdomain>

APIcast gets the correct value from the configuration fetched from system using THREESCALE_PORTAL_ENDPOINT environment variable. So setting BACKEND_ENDPOINT_OVERRIDE is not needed when deploying APIcast outside OpenShift.

The request is to update the chapter 3.7.3. Connect APIcast from Other Deployments.
APIcast can be deployed and connected from other deployments but no need to use BACKEND_ENDPOINT_OVERRIDE.