The essence of the problem.
1. You have a private intranet
2. You have a server under CentOS, only available from this intranet (A)
3. There is a computer under Win7, with access to the intranet through a specific VPN (a custom build. the decision, binding on the Mac address, to run on another machine it's impossible) (B).
4. (B) has free Internet access via Wi-Fi office
Task: to make it possible for any computer on the same network, and (B) to work with the server (A) using a VPN connection (B). Probably some hitny ssh tunnel or something similar. (C) you can install the software. (A) very limited (to raise private VPN impossible).
I would be grateful for any hint.