How to pass Userid to webgate protected OBIEE when using Anonymous Scheme

We already have OAM 12.2.1.3 with a OHS 12.2.1.3 webgate fronting OBI 12.2.1.3 in SSO mode working.  We actually have two webgates, one for OID authentication and another for SAML authentication.

We would like to set up another webgate that would protect the analytics resource using the Anonymous scheme (basically allowing all unauthenticated access) for public access to a specific dashboard only.

The issue is that we still need to pass the public user id that we created (OBIPUBLIC) from OAM to the OBI app so that it will handle it in the same way as if it went though an actual authentication.