Not sure why its taking so long. Flashing the new operating software (240E) takes 5 minutes and flashing the tune takes 5 minutes. So ten minutes and you have new software and tune, no charger required.
Edit: nvm, maybe they are using a different tool. You can connect a charger to the terminal under the hood (red tab) and ground to any unpainted metal - or use the terminals in the truck on the battery.
You could also connect another (started) car using jumper cables if a charger is not handy.