If it wasn't fitted at the factory the minimum you would need to add is a new ESP type ABS block, a steering angle sensor & a yaw sensor. That's assuming all the wiring is present.
Unfortunately you cant just fit the button and activate it.
The Accelerometer sensor is usually fitted in the front centre area of the vehicle under the front centre console gearbox. Although the gear shift may be mounted on the dash, the Yaw sensor is usually near the location of the gear shift near the floor.
As for the ABS / ESP pumps, it is the ECU fitted on these and the software they incorporate that you also need to be concerned about, but will also need to make sure all the associated systems and ECUs and software are compatible as well as the programming. Not something I would tackle to be honest.