Just for the heck of it I checked the service manual. There is of course no mention of disabling sata, but I found a diagram of the logic board showing the K2 I/O device and disk controller. It controls the internal hard drives, the optical drive, modem, ethernet, firewire, usb, bluetooth, audio circuitry and connects to the PCI and AGP busses. All I/O functions...... so I don't think you want to mess around with that.
Dual 2.0, 4 GB, 1.3 TB, SuperDrive, 9800 SE, 20 Aluminum - 15 1.5 PB, Mac OS X (10.4.8)