Я рекомендую использовать remotefx, если это возможно.
The squid proxy log isn't really designed with giving you the type of detailed user activity logging your thinking of. Yes you can use Sarg to get a general idea as to user cache activity and traffic. However it will never give you the kind of granular detail your manager wants.
I would recommend trying LightSquid it provides more detailed reports then sarg if configured correctly.