Hi, you could try blocking the IP address in your routers firewall or in the hosts file of windows PCs.
IE: add the line 127.0.0.1 18.104.22.168
Or the line 127.0.0.1 www.bbc.co.uk/iplayer
You may end up blocking more of the BBC site than you intended though. Still worth a try you can always undo the changes if you don't like the result.
why are you trying to block Iplayer
From September, you need a TV licence to watch any programmes on iPlayer.