Well, if drophacking is possible by blocking the opponents IP just do the following ...
1) alt+tab out of the game and enter the DOS command window (start -> execute -> "cmd");
2) within the DOS command window, simply enter "netstat" in order to receive a list of established connections including IPs; figure out which of the IPs is one of your opponents;
3) enter your router-menu and add the IP to the blocklist; eventually a software-firewall will do so, too; save the changes et voila, the opponents IP is blocked and his client should now freeze.
I haven't tested it, but thats the way you could easily do it.However, I have heard that freezing opponents clients is possible within the game itself. Rumor or truth, I don't know.