[keycloak-user] Map SAML Subject NameID to user email

Hi guys, I have a requirement to map a user email to the /saml:Subject/saml:NameID field in a Keycloak SAML client. I can see that someone else is asking for the same at http://stackoverflow.com/questions/39854398/sending-username-emailid-in-t... without much luck. The mapper only maps attributes while I need to change the subjects identifier. Could anyone help with a thought on how that can be achieved? Many thanks, Niels