Email address as user ID

Hello all, we are looking to use the e-mail address in the portal for external users as the userID... the issue we are having is that we want to connect to some SAP ABAP data sources... The portal is 7.0 and al ABAP sources are going to be 6.40 and 7.0... is it possible to setup the UME to have the "R/3 User of the MYSAPSSO2 Cookie" on the SSO ticket pull the user ID from the LDAP or somthing simmilar??

D.