i don't know the situation with AMD CPUs. But with Intel, unlocked CPUs can be overclocked in Windows. Since it's done from the OS I don't see why it couldn't work with AMD also. That doesn't mean it HAS been done.
The method is to use Throttlestop software which is designed to undervolt, and underclock laptops for battery life, and use it's Voltage and multiplier controls with an unlocked CPU to overclock. The Dell Dimension E520 in my sig. was overclocked using this method. The link is at the bottom.
You might ask this question at Notebook Review, or ThechPowerUp in the Throttlestop threads. if it's been done with AMD they would know.