This is not an elegant solution but it does work.

When I created the bootable SD card I made another on a USB thumb drive. I connect my SATA hard drive to the Acadia, insert the bootable SD and boot up. Once booted insert the thumb drive. Next I use dd to copy thumb drive contents to the hdd. Use Gparted to resize hdd partition to fill the empty space. Once these things are done then we are ready to get our hands dirty by editing uboot environment variables.

I connected a FTDI cable to the debug port of the Acadia. Settings are 115200,N,8,1. Reboot Acadia and you should see u-boot pause for a few seconds. Press any key to stop the boot process and enter u-boot command line.

At the u-boot prompt enter:

u-boot>setenv bootarg_mmc 'setenv bootargs ${bootargs} root=/dev/sda1 rootwait fec_mac=${ethaddr} video=mxcfb0:dev=hdmi,19200x1080M@60,if=RGB24,bpp=32 fbmem=28M'

u-boot>saveenv

Upon reboot the Acadia will start the boot process from the SD card but the filesystem on the hard drive will be mounted as root.

If anyone needs further information I can break this down into smaller steps.