Um, you don't. That's the point of a firewall. And you put your job in danger if you start hacking at work, because the chances are that they will monitor the traffic and when they see an increase in video downloads heading in your direction they'll (a) just block it and/or (b) report you for misuse of company resources, and the more you bypass the firewall and create work for them the more likely you make b to come true (and the less trustworthy you make yourself appear, so even if you don't get fired your reputation at work will be tarnished for some years). So the best bet is to download the videos etc at home and just use your work computer for work.
The good thing about bittorrent is that it doesn't matter too much if you have a slow link; just set stuff going and eventually it will arrive, if you leave your computer on all the time of course. Even throttled at 15Kb/s I can download far more stuff than I can possibly watch.