>>is it possible to setup BarbaTunnel to forward traffic to a port on another host?
I don't understand what you mean by "another host"! p2p Internet-Tunneling always need a server or by other word another host.
by the way If some of your users could not connect to your VPN server, you can simply use barbatunnel HTTP or UDP or Redirect tunnel to solve this issue. In worst case BarbaTunnel HTTP-Tunnel will work, I didn't still see any network firewall to able to
block it yet. Make sure you local system firewall does not block it, its good idea to stop local system firewall both client and server side just for test then enable them.
Just follow quick start and try to establish the VPN.
Let me know if you still have problem.