The correct procedure for this is in the manual btw.
Pop the tow hook cover out the front bumper. Behind it are a couple of leads. Connect these up to a spare or near by 12v source. This should be enough to unlock the doors I think then you are in, can set tow mode, open charge port for real power etc.
Many AA and RAC vans now can hook you up with a few kwh at home charger speeds too, which is then enough to get you to a real charger and get going again.
Check all this in the manual, but it's there. I think I have a printed copy of this and one of the other emergency procedures in the car (yes, I see the futility of this, but it does mean I remember it exists)