As topic says, you can create a death knight on any server without having a level 55+ character on it!
You'll need a level 55+ character on the account you're going to do it on.
Okay, so first of all, go to the paid character transfer site. Select the server with the 55+ character, and then choose your destination realm, enter your credit card information etc etc. Your credit card will NOT be billed until you have approved the mail you'll get aprox 20 minutes later (may vary between servers), but a copy of your character (unplayable) will show up on the destination realm. so log on your account, create a death knight on the destination realm. Then cancel your transfer, and voila, you'll have a level 55 death knight on the destination realm without having ur other 55+ character there!
Hope you got what i said, I'm in a haste, gonna play some wotlk before school loels
PICS!
Original Realm
Destination Realm