"day dream" is the only thing close to being able to keep the screen on while charging.
pretty much the same effect as the screen going asleep. only difference is there is one less step because you dont have to "wake" the phone up, then unlock the screen. you simply touch the screen and you are right back to where you left off. click the gear icon beside any of the choices for more options as far as what you want to display.
i dont have a password or security pattern set up on my phone so im not sure if it comes into play on day dream mode. this is yet another drop of the ball by samsung. unless someone knows something that hasnt been posted yet.