Refer field for user lookup

Refer field for user lookup

Hi,
I've been experimenting with refer fields for user lookup for different templates and have run into an issue.
We have a fairly large user database (10000+ users) so there are several users with the same first and last name.
Do you have any suggestions on how to distinguish users with the same name?
One solution I've tried to implement is to list additional user info (login id, e-mail address etc.) in a text field. In the case of several users with the same name the requester then has to delete the unwanted users from the text field. This is a rather sub-optimal solution so I hope you can provide a better solution.

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