Is the firewall a router or is software running on the machine (like the Windows Firewall)?
There are tunneling services like your-freedom.net that will get around firewalls, but the free version will only let you download only slightly faster than dial-up and only for an hour at a time.
There also services like
Furk.net which will download it to their server and let you download it in your browser.
Finally, you can rent your own server and download from it.
There not much in the way of free that will be very useful.
Edit:
Thanks to
20 BitTorrent Tips and Tricks | TorrentFreak
I found
Whalesalad » Tunneling BitTorrent over SSH
you can get shell account for a dollar and tunnel bittorrent through ssh.