Shoot the "real" character acting alone, then have them leave the frame and without moving the camera, shoot the "Ghost" performing their action with the other actor standing where they were before. Using After effects, Shake, Nuke or just a garbage matte in FCP, PP, Vegas or Avid, add the second layer of footage above the first and drop its opacity to 50% or so and use the matte (or rotoshape) to mask the hand where it overlaps the "real" character so you can ghost it over the bottom layer of footage. You'll probably end up with these layers of footage:
50% opacity - just the ghosted Hand where it overlaps the "real" actor
---------------------------------
50% opacity - ghosted actor cropped at the point where they reach "into" the other actor's chest
---------------------------------
100% opacity - "real" actor