Ok. Open KNetworkManager > Manage Connections > Wired > Add. Select "Limit to interface" and specify the connection appropriate if needed. Specify any other needed settings ( such as a static link ) then accept, and accept again. You should now ( this is even easier to handle with the Plasmoid though ) be able to see an item in your menu which has the name you gave to the connection.

Limiting it to one connection should help avoid the crash.