Hi there,
That's not really advisable for a laptop. The thermal solution is 'just about enough' for the components they house. Pushing more heat and voltage through an already tight chassis will most likely not bring the results you want, and may cause other issues for you. In desktops, there is additional room in most cases, and along with case fans, can take an overclock on a CPU/GPU, and dissipate the heat better.
I would advise against it.
To answer your question though, yes, it's possible to OC the GPU. Safely though? That's a different question.