How can I use a system.img from a different location to restore a board?

I am following the cloning guide on http://elinux.org/Jetson/Cloning
I backed up a TK1 to a usb flash drive.
Now I’d like to restore this to a different Tk1.
I’m using:

~/Downloads/TK1/Linux_for_Tegra_tk1$ sudo ./flash.sh -r jetson-tk1 mmcblk0p1

I am assuming it is looking for system.img in the current location, but my system.img is in a different location (/media/… - the mounted USB drive).
Looking at the arguments for flash.sh, not clear how I can override the location of system.img

any idea?

I created a soft link from the bootloader folder to the different location and that did the trick:

~/Downloads/TK1/Linux_for_Tegra_tk1$ ln -s /media/.../system.img bootloader/system.img