That's impossible, the wifi will also connect to the same server with the same restricted sites. You would also need to create a secured access with a password which your network admin would no doubt be happy to quickly provide to you.
Ask your the network admin, ask him how you can keep an eye on your private activities while in the office.
What you are asking is nearly impossible for the AVERAGE USER, so lets just say it doens't work like that. Unless you are prepared to build static routing in your LAN, then you cannot do what you are asking. Plain and simple. You are basically LOOPING your networks!