I have to agree with Cadence here. People can never change into something they are not naturally. Perhaps when we talk about "turning a vanilla" what we are really doing is simply drawing out the Dom or sub that is buried inside of this person. These forums are littered with folks that talk about having feelings and notions that they were either Dom or sub, but not knowing how to express these feelings or being unnerved and embarrassed by them.
In my case, I knew I had sub leanings but was never fully comfortable being submissive to a partner. As a result, I usually ended up topping in the relationship - I was less vulnerable to the unknowns of my personality that way. Still, there was the desire to be dominated. When I met J-Go I knew very early on that he would be a partner I would give myself to. He, however, had even less r/l experience with BDSM than I did. I hinted at my fantasies, and opened the doors to him asking questions of me and so on. We started with light bondage, then stepped it up little by little, always communicating and talking after each scene to let each other know what worked and what we wanted more of. We've been together now for a year, and my how far we've come...The only thing left vanilla in my house is the pint of Haagen Daaz in the freezer door...