VPN on Mac with two interfaces

I have following setup: MacMini connected to internet through wired interface, wifi is set for sharing. E.g. wireless devices connect to MacMini and use it's internet connection. Question How to setup vpn connection via wired interface only so all wireless connections will be forwarded to a new virtual location? PS: tried with Cisco vpn client, it connects, but all traffic over all interfaces go to vpn. E.g. can't act as a bridge.