It would be great if all us submissives would enjoy pain... at least from the perpective of our dominants. Unfortunately, if it isn't natural, then I have my doubts that you can "train" someone to like it. It's kind of like brussel sprouts; either you like them or you don't and no matter how much you sugar coat them, they're still gonna be brussel sprouts.
I dislike pain. There are a few activities that I enjoy that involve a certain type of pain, but I am, by no means, a pain slut and no amount of training is going to change that for me. Her pain tolerance may increase, but probably not her enjoyment. That's just my view on things.