SSO2 logon ticket with alias

Does anyone know about an SSO2 ticket that can be issued by the SAP Portal and contain an alias, which can then give the user a default identity and an alias identity ?

Until now "login with alias" is only available for the basic login module, however we would like to be able to issue an SSO2 ticket fom the EP and accepted by a backend system where the userids in both systems are different. (We don't want to use "EP userid mapping" !)

If anyone know any details please comment. Thanks.