First, I disagree that "show don't tell" is a maxim that must be followed at all costs in all fiction writing.
Second, if the POV can't show anything you have no story, so consider some ways you can show.
First person is going to give you a very strong voice but with two first person voices it could become quite confusing for the reader.
As far as how the POV can show with no body:
Perhaps the POV does not lose all control at first, but rather slowly as the player gains control. Or the POV is constantly fighting and can occasionally move one extremity to cause violently hilarious situations. The player can also evidently "hear" his voice, right, so the POV can be saying snide things like "If I had control of my left eyebrow, I'd be raising it." Or the player could feel a chill up his spine or sneeze unexpectedly. Or become dizzy. Various mechanics could be used, and you could always consider that the taking over of the POV blends their minds in a way that it is difficult to tell one from the other, both from the player and POV's perspectives.