How to null route an IP or website
To null route a website, you'll need access to the DNS editor. There you'll change the A record to point to: 127.0.0.1
To null route an IP you'll normally use the shell command (if the IP to block was 65.21.34.4) it would be:
route add 65.21.34.4 gw 127.0.0.1 lo
Essentially directing the IP or website DNS to 127.0.0.1 will null route the IP.