Have not done this .... so this is just thinking out loud ...
How 'smart' is your SMTP server? Could a rule for incoming mail from 'noreply@moodleserver' with subject line that begins with 'Welcome to' .... blah, blah, blah ... (subject lines have some static phrase, do they not? ... like 'Welcome to") be written to bcc to a generic 'registrar@something'?
'spirit of sharing', Ken