Using username at example.com and plain username

[Kriston]

I have users who log in as "username at example.com" and just as "username".
How do I append @example.com only to those users who don't have @example.com
already?  I have a fairly generic FreeRADIUS 2.1.10 installation that
connects to a MySQL server.

I've tried a number of different things in dialup.conf but none have worked.

Example 1:
sql_user_name = "{%{Stripped-User-Name}:-%{User-Name}}@{%{Realm}:-example.com}"

This results in a string in the SQL queries for User-Name that looks like
"=7B:-username=7D@=7B:-example.com=7D".

Example 2:
I have also tried regular expressions like this:
    if ( %{User-Name} !~ /.example\.com/i) {
        sql_user_name = "%{User-Name}@example.com"
    }
But this one results in a blank string for in the SQL queries that use
sql_user_name.

I'm open to any and all comments.

Thank you.