Had to do a little freehand scribbling to remove some company stuff and extra distracting functionality, but I'm pretty sure this will still work.  Execute the code thus: 
$ php email2uer.php jdoe
It should just come back with something like:
johndoe@yourcompany.com
(or warn you that this user id isn't in the Phabricator SQL database...)
Then use it however you'd like.  Thanks Chad and staff for your patience.
========================================
<?php
$root = "/Users/yourinstalldir/phabricator";
require_once $root.'/scripts/__init_script__.php';

if ($argc !== 2) {
        print "Usage mail2user.php <username>";
        exit(1);
}

$username = $argv[1];

$existing_user = id(new PhabricatorUser())->loadOneWhere(
        'username = %s',
        $username);

if (!$existing_user) {
        print "*** ERROR - username $username is not a valid Phabricator user.";
        return 1;
}

$PHID = $existing_user->getPHID();
$existing_email = id(new PhabricatorUserEmail())->loadOneWhere(
        'userPHID = %s',
  $PHID);

$address = $existing_email->getAddress();

print "$address";

return 0;
?>