Portal authentication using ldap and SAML - switch fields

Is it possible using SAML or something else to get the Portal (7.01) to authenticate with SamAccountName and then provide another parameter for use with the SSO connection to the ERP back end for use in ESS/MSS? I do not want to use User Mapping as it is a manual process. This needs to be an automated process where user authenticates with email address but account id is actually used as the login id for the portal.

Thanks

Paul