I'm going to say that that is a non-standard use of "separate values", but I'm sure others have done similar too.  I would use jQuery and when the user is selected, you pass the user ID, via an Ajax call, to a PHP program that looks up the user and returns his/her email address and unique number.  The jQuery code then sets the value of the two read-only fields to the values returned by the Ajax call.  Another option, using jQuery without the need for Ajax is change your "separate values" to be "email_address[some delimited]unique_number", e.g., [email protected]|456.  When the user selects a value, you can use jQuery to split the string by the delimiter and assign the values to the read-only fields.  That being said, two things: 1. I'm not clear how you set up your separate values in the first place and 2. There may be a way without any custom code, and I'm not thinking of it.