I hear there's a Chrome extension called Zenmate that basically proxies you to blocked websites, and be sure to use incognito mode. The IT department can still see the web traffic that shows a proxy was accessed, see which machine it was done from, and see who was logged into that machine at the time, so don't think lets you browse with impunity.
If you're accessing it on your phone or a tablet on the company wifi, they'll still have a log of the device's mac address and that it connected through a proxy to probably something that's banned. If they use mac address filtering and you had to register the device to get on the wifi then you're totally busted. Otherwise they'll probably just ban its mac address and you can either accept defeat or you can go ask them to unblock you and basically turn yourself in by doing so. They'll probably have a good idea of what floor/department your device connects from and the device's manufacturer with a little effort, so you may get caught regardless, especially if there's a high level of data security in your line of work such as medical or financial.