VPN Tunnelling Using MAC Address

I was informed by a gentleman that you could create a VPN Tunnel using the servers MAC address as the connection. This would help solve a lot of problems with a ADSL connect between two offices under the same provider. They are wanting to connect them together but they are being issue Non-routable address, also it will cost $40 a month more for static address. I need to know if using a MAC address in VPN is possible and how