Well it really depends on the technology that the block is using. It's possible that the blocker is client side (easy to deal with) or server side which is a little more difficult...
Do you know the name of the blocking software that they use and whether or not is installed on your work computers? Your other option is to use a proxy which is slow and risky. I'd love to help but I need to know more about the particular software they are using. In the meantime, you could try using the Corel Content Distribution Network (google it), SSH tunnel into your home computer or buy a cheap VPN.
However, your really rolling dice and dancing on the dark edge of serious punishment if you get caught... if you don't know what your doing, I'd just use your mobile phone or wait till you get home. I mean that probobly won't stop you from trying, but keep that in mind, you could get fired. The administrators at your employer will surely be logging everything that happens on their network and all it takes is one red flag and they can go back through everything. I've seen it happen too many times...