I don't think you can, depends on how lucky you are. But their might be a trick out there...
You can. But you have to join the same time as another person.
So it's really hard.
All you have to do is go to "Game Instances", And then look for a server that has one less than the full number (Like, 15 out of 16). Then, You have completed the server, and now it is full (Well, Once you Join)