Can you be more specific on the laptop, there are several Custom Pavilions and the more expensive ones have the possibilty to choose the GPU. Still looking if it still can be changed later, i'm not sure of that. The best choice there was a 6770, it should be faster.
Took some time but i still can't find out if it's possible. Even contacted hp but i'll have to register and stuff to get an answer. Maybe you could try that yourself ? Or just try to open the case and see for yourself if there is a seperate gpu you can take off. It can be quite difficult though with some laptops to get it open.