Virtualbox with Win7 as proxy

I will try to post my question as simple as possible.

Problem: I have a linux (CentOS 6.6) pc and I have to access to different servers, svn and git repositories that are accessible only through a VPN client that only works on Windows.

So i have to use the guest machine (windows 7, virtual box 4.3) as proxy, gateway or whatever thing that allows me to redirect all the packages from my host (linux) to that machine.

One important thing to mention: I cannot use bridge mode.

Thank you for your time reading this !