I currently work for an employer who trains employees on a new keyboard layout. It's a pretty big operation, and they've trained thousands of people over the years, so I figure they know a thing or two about how to go about it. Basically what they do is, start the person on lessons for four hours a day. Once the person attains a certain baseline speed and accuracy, they send that person onto the floor to work and (ideally) build up to a higher level.
A reasonable extrapolation from this would be to start out with just lessons for a few hours a day. Once you'd hit some reasonable benchmark (say, 35 WPM at 96% accuracy), then go cold turkey, pushing yourself towards a higher benchmark (say, 70 WPM at 98% accuracy). At that point, you can just coast, or push higher if you want.
Doing it this way, you avoid the main problem with cold turkey: being completely helpless when you start out.
Of course, employees can type whatever they want at home, so it's not 100% cold turkey. I would advise against 100% cold turkey, anyway. Why swap one skill for another when you could have two skills? Why have no choice when you could have choice?