for those on ivy systems the fix could simply be enabling (bios) the intel internal graphics and setting it to be initialized first, with or without attaching a monitor on any of its port. the thing with this setup is you will not see anything on the monitor hooked to your 7xxx during boot. that monitor will only come alive when the login window arrives, wide awake and waiting for your password.
the intel graphics need not have its kext loaded, at least not in my setup. though without its kext loaded i lost sleep, not me but my ihack. i regain sleep by injecting igpu into my dsdt as described by proteinshake below:
i used "AAPL,ig-platform-id" = 0x06, 0x00, 0x62, 0x01, which is from a real imac13,1 with a core i5 3470S. i didn't inject the other info only "AAPL,ig-platform-id".
while the intel hd 4000 driver and capri fd loads for my hd 2500, it does not make any monitors attached to its ports work. i think this is how it's supposed to work with real imacs that have hd 2500 on them, imac13,x with core i5 3470S/3470 and such. it seems to me the drivers are loaded for use with airplay mirroring only. i do have the airplay mirroring option showing/enabled in my system but unfortunately, it is unable to actually mirror anything on my atv even though the atv works as an audio output device. i'm hoping this will eventually work when 10.8.3 is released or when someone finds the recipe.