Well, Much to my suprise it looks like pin 34 of the IDE connetor does not assert a signal if the cable is 40 pin and does assert a signal if the cable is 80 pin. This is a standard for all motherboards that support ATA66/ATA100. Now I just have to figure out where this signal is asserted too (maybe a GPIO -> in). Once I figure that out this will be easy. I can just tell coreboot to: read ide cable signal, set ide cable select register bit to 1.
Thanks - Joe