Humans are exceptionally adept at learning and operating new machinery. Let's get an example that everyone knows, if not has experience with. Computers! They have a multitude of ways to operate them, and we can learn to operate an absolutely incredible amount of different things.
Seeing it in action is easy. Watch someone type in a text program for the first time, then at someone adept at it. Pne is taking an incredible amount of effort, the other isn't even thinking about typing, but is just making the sentences as the words materialise on the screen. In games we have a ton of different movements. 2D, 3D, walking, flying, driving, operating weird machinery. The list is endless.
An interesting study about brain augmentation showed people can learn how to move a mouse on a screen. I cannot remember if it was the hand or arm they moved, but this was translated to the mouse. After some time they had learned to move the mouse without moving the arm or hand. They could thus use the same part of the brain controlling different things.
This means that as long as someone can have feedback on the workings of an organ, it can be learned at used.
Do keep in mind that it isn't 'free'. Brain areas are being used, making the traffic in the brain higher and possibly shutting out other things at moments. But learning and using an extra organ should be less difficult in most cases than learning how to control a character in a game. The functions and translations required fir a gane are generally much higher (movements, interactions, etc through fingers and different kinds of controllers).
Worst case scenario you "just add some extra brain matter".