Mac OS X Mountain Lion cannot share internet connection because of 802.1X protection
I agree with Gordon. The 802.1X security measures are in place for a reason. You should contact your IT team to see if they have other options for you or if they can set up a guest network. In the absence of that, I would recommend getting a MiFi from your carrier or turning your smartphone into a wireless hotspot. If you have access to LTE, it may be faster than your office WiFi.