I am running Windows 7 on a virtual machine. I have VPN Gate installed on this machine. This VPN software creates a virtual network adapter and configures it with an interface metric value of 1.
I have configured VMware Player to use NAT network connection for the machine and I've set its respective network interface metric to 1337.
So when I connect to VPN Gate's relay servers, Windows detects a new network and uses the IP assigned by the VPN and not the shared IP of the NAT (overridden by the interface metric). When I'm not connected to the VPN, Windows uses the IP assigned to the host (i.e. IP assigned to me by my ISP, shared through NAT)
However, I want to know if there's a way I could override the NAT completely and make it such that Internet access is only available when I'm connected to the VPN. For when I'm not, I want the web browsers (and all other Internet enabled apps) to think that I'm offline.