Other than they can't be banked, borrowed or transferred-again, once they are in your account, you can use them just as you would any other point….no other restrictions, so yes, you could use them to make a ressie, then add that additional person to the reservation.  In your example, the reservation never really ends up in somebody else's name regardless if you are using your own points or rented points, you merely add them to the reservation, as you the owner always retain ownership of the ressie.