A bit late but I think I understand what mac wants.
Yes, it is possible to create a 2-way tunnel using an Access Server and one Linux client.
The tunnel itself will be initiated on the client machine, and terminated on the Access Server.
Traffic can pass in both directions over this tunnel.
Routes can be configured on the Access Server to allow traffic from networks behind the Access Server to reach the client and the networks behind the client.
Routes can be pushed to the client to allow traffic from networks behind the client to reach the network behind the Access Server.
The interesting thing is that the routing on both the Linux client and the Access Server can be managed from within the Access Server's admin UI itself.
In particular, you will want to use the VPN Gateway functionality found under user permissions in the Access Server's admin UI.
That means that as far as the Access Server and the Linux client are concerned, all the routing will then be okay.
Of course, any routing required on the networks behind the Access Server and behind the Linux client will still need to be done in these networks.
Also, the Linux client must have IP forwarding enabled, as must the Access Server - but the Access Server has this enabled by default while the Linux client might not.
There are 2 guides available, one for Layer 2 bridging, and one for Layer 3 routing - this last one appears to be the one you want:
Layer 3:
http://docs.openvpn.net/how-to-tutorialsguides/virtual-platforms/site-to-site-layer-3-routin-using-openvpn-access-server/
Layer 2:
http://docs.openvpn.net/how-to-tutorialsguides/virtual-platforms/site-to-site-layer-2-bridging-using-openvpn-access-server/
Good luck.
