ATI/Intel switchable graphics?

I’m having trouble tracking down any information on ATI/Intel switchable graphics. On Nvidia/Intel combos, I just have to extern a variable to indicate the application should use the discrete GPU:

extern "C" {
_declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;

How is this supposed to be done on ATI/Intel combos? I have consulted the Google and found nothing.