Same set up just reversed.
Getting the USB through the hole and into the car it the trickiest part, I used a piece of thinner wire and fed that through.
Once the wire is through tape the USB and pull through gently.
Just make sure you have disconnected the battery!! First feed the USB cable through the firewall... then reconnect the ecu and jb4, connect the usb to the jb4 unit, and LASTLY re-connect the battery.