You could try these methods;
[http://www.wikihow.com/Fix-a-Stuck-Pixel-on-an-LCD-Monitor|WikiHow] - Use care here on doing this as you don't want to make things worse!
[http://www.apple.com/downloads/dashboard/status/pixelfix.html|PixelFix] - This widgets is the best software solution I know of.
If either fails then it's a question of cost of replacing the LCD Vs living with it. One stuck in the middle 1/3 of the screen I would likely replace otherwise I'd leave it alone.