Just to make this clear, I am not telling you to have two WoW accounts for this trick. This is for just one account. This is also obviously not possible on a PvP server.
You will need to open two WoWs.
Grab all the horde and alliance characters that you own and put them all in a convenient location where they will res in the same graveyard.
Now put your username and password into the first client, login and flag PvP.
Alt-Tab to the second client, login quickly and select a character of the opposing faction.
You have about 25-30 seconds to burn your other character down as quickly as possible and gain an HK. You may cycle alts to maximize this.
The server disconnects you from client 1 and begins the camp countdown on that character when you login to client 2. Because of that, client 1's character hangs there for a half-minute. You can expand this trick's use to buff your alts for grinding and stuff.
Enjoy