There is supposed to be a working unlocked BIOS for your board here in this thread from another forum.
I am not suggesting you download it, use it, and take no responsibility for it, but it might be what you are looking for, proceed at your own risk!!!!
This is why we build our own systems, as most prebuilds do not include the features in the BIOS for overclocking. You will also void your warranty if you do this. http://www.bios-mods.com/forum/Thread-ASUS-P5G41T-M-LX2-GB-Unlocked-Hidden-Overclock-Capabilities