I'm pretty sure that it cannot be done, the processors are usually soldered into the system board and since the BIOS is proprietary and manufacturers do not want laptops overclocked there is no option in the BIOS to alter the system board settings. Even if it could be done, laptops generate a tremendous amount of heat even without being overclocked, given the space and airflow constraints I don't see an overclocked laptop having much chance at stability.
Zenmervolt