The key point is that on Cisco VPN it can only be changed by the people controlling the VPN head-end. You can't just add a route or remove a route and influence the VPN in this way. It's highly likely that if the VPN is configured to send all traffic across the tunnel, the company is doing that intentionally to ensure that they can run the traffic through their content filters, URL scanning, etc. as they would if the user was in the office. In this situation it can be very difficult to overcome.