I don't think you have to unlock them, you just have to know what they are. Last night while the game was still installing I did both of Kitana's on the very first and second matches of the ladder. I definitely didn't have the second one unlocked and it did it. Honestly I don't even know what motion I did to do it, it was just some sort of muscle memory from previous MK games.
Maybe it locks them though when the game installs, I'm not sure since it was still installing by the time I went to bed.