How to securely erase an arbitrary SATA drive, utilizing the drive firmware to do so?
There are three ways of dealing with it:


OS X provides good userland access to any USB device, so if one wished to bundle hdparm with a USB storage driver, it'd be possible to use hdparm on USB-connected devices to perform secure erasure.
Alternatively, you could write a kernel driver to expose this functionality to the userland.
Finally, you can use a virtual machine running linux, since both VMware Fusion and VirtualBox expose USB devices to the guest. I'll detail this last solution here.


The steps are:


Buy a USB 2 or USB 3 hard drive enclosure. I've verified that the NexStar NST-D306S3 dock works great.
Plug it into a USB 2 port. I never got it working with USB 3 ports, due to bugs in Linux kernel.
Set up a new VM and attach systemrescuecd image to the virtual CD drive. The VM does not need a hard drive, and needs only 256 MB of RAM.
Boot up the VM. Attach the drive to the VM.
Ensure that only one USB device is attached to the VM. This storage device will be available as /dev/sda.
Issue the following commands on sysrescuecd's console:

hdparm --user-master u --security-set-pass NULL /dev/sda
hdparm --user-master u --security-erase NULL /dev/sda


That's it. Your drive will be completely wiped by its own firmware, without using any appreciable amount of USB bandwidth, CPU, nor drive's write endurance (for SSDs). This works perfectly even on the earliest Intel Mac, and won't slow the machine down any. You can use VMware Fusion or VirtualBox, both work equally well for this purpose.