SSO between Two SAP Portals

Hi,

I am having one SAP portal connected to ECC/CRM/BI. The userID in the Portal UME is emailID's  and is mapped to the respective users in backend systems. The userID's in the backend systems is employee number. We have configured it with "Single Sign-On using logon tickets with user mapping". The reference system used was ECC.

I now want to hook up my BI portal to the SAP Portal. Since BI Portal has BI ABAP as UME, all users are maintained as employee numbers. How do I setup SSO between these two portals which have different userID.

Thanks,

Mark