If you had no screen how would you know where you are clicking? Yes the wiimote will see where your led is in space but you wont know where you are clicking or what you are clicking

In that case, theoretically it would work. The hardest part would the actual calibrating part, because you wont know where the dots for calibrating are. Once you have successfully calibrated the wiimote, you would just move the led pen in the air and the mouse would move on the screen. Also another thing to think about is the fact that when the wiimote sees the led, it interprets that as a right click. So you are just going to be right clicking all over the place.
Usually when you are doing the wii whiteboard, you only have the LED on when you want to right click. But in your idea, if you did that, you wouldnt know where the mouse is because the wiimote couldnt see it.