Yes. I have Internel connected with DVI and ATI with DP on my monitor. So I only need to switch Input.
I managed it now also to boot with HD7000 directly if I set Display to Auto. But then I also get the white screen that can be solved with sleep. Both not perfect ways but for now I´m satisfied.
Great News,
for me the HD 7950 with Build 12D76 (10.8.3) is completely running. I testet Diablo 3 and it runs great without graphic issues.
I also get no white screen but I can only boot into chameleon with Intel onboard card (in bios IGFX first). If I boot with HD7000 directly I get a boot0 error.