Just see the sd.img that contains the OS and weighs more than 8GB, so I can not imagine extracting only the bootable parts of that IMG and redirecting many things to the USB port of the DOck to execute the rest of the IMG file. So I am doubting if there is only USB support after having to configure all the OS (which is not advisable to do it in the coupled mode). So my doubts are already being answered ... anyway I wish you good luck in Boot the rest of the IMG from USB-HDD in the docked mode.@Ghost92, however you can use USB drives as partitions to store data apps and stuff on them
I'll try to resize and move the partition where the OS is currently installed and move it to the external hdd while using the SD card on the switch to boot the bootloader files and so on.










