There's an option (configured by whoever has admin rights) to allow a set amount of time each day for "shopping" sites etc. At least there is on the NATS intranet implementation. They added a button that lets us have 60 mins a day of "reasonable use". Still (quite rightly) blocks the dodgy sites though.
Have a word with your IT admin and see if it's possible to have that added.
Otherwise, you're stuffed.
ST