Scientists have come up with a way to restore sensory functions to people who have numbiness or general loss of sensation in their toes and fingers. The article doesn't talk about this, but if you think about it, it could really be the key to getting the brain to learn how to control a cybernetic limb.
Where the limb would connect with the body, there'd be some sort of inductive electrodes that would send signals to the nerve endings in the stub of the limb. Using the method in the article, the degree of control over the limb could be vastly enhanced. Not only that, but it seems that normal people could gain better than 100% sensory functionality by using the drug and doing the activity you want to remember the motions for. I mean, I could seriously kick ass at some video games on this stuff!