You could remotely execute command removing all the interfaces of your connected users with a cronjob.
Login with ssh/telnet -> remove ifaces and wait for calls from angry customers.
I wrote a shell script for remote login and command execution.
It works with both ssh and telnet.
It's bit fancy since I also included dialog menus (I had some spare time).
The whole thing can be easly changed to make it more suitable for running within a cronjob.
Just read the connect_ssh and connect_telnet functions.
The script is avaliable at:
http://yazzy.yazzy.org/coding/shell/rou ... uteros.txt
I tested it with sh on FreeBSD and Gentoo Linux (where /bin/sh -> bash).