OpenSUSE Network :: Blocking Outgoing Network Traffic On Workstation?

As too my question, at this time I dont control the router/firewall an I would like to block a port thats used for guild wars on my workstation for a while. The reason for blocking is children have abused it an lost it.In this case I am trying to block outgoing traffic on port 6112. I have tried setting up a proxy server on the workstation, but the game seems to ignore it an jump on. Due to the environment, I enabled the workstation SuSEFirewall2 firewall an tried setting up "lo" as a internal an configure the firewall as a router, then disable 0/0 an configured for 0/0,tcp,443 an re route port 80 traffic to proxy.

When I had my own internet, I had a transparent proxy enforcing rules for access times. So setting up a proxy on each machine would not be a bad thing, even if it took some creative thinking. I am trying, but seem to be missing something.Ideally, I would like to setup a transparent proxy, as my kids have learned alot about system administration an know to check the proxy module. If all they have to do is un check "Use Proxy" an by pass a local proxy server, then I am kinda defeated. An applications such as firefox have a proxy setting they could set to none instead of system