Multiple ldap_uids per user

Hi
I've a Nextcloud install with integrated OJSXC xmpp client. The Nextcloud install relies on LDAP for user authentication and lets them use either their ldap uid (firstinitialsurname) or mail address (firstname.surname@sld.tld) to log in.
The problem I'm running into is that to Jabber firstinitialsurname@sld.tld and firstname.surname@sld.tld are 2 different users and so the web chat client gets different rosters depending on which attribute the user has used to log in.
So my question is how can I turn

Into something like