Ah, good idea regarding trying to fashion something to tug on a door handle, but he's already tried that!
Apparently when he tugs the driver's door handle from the inside, or the rear offside door, nothing happens! Odd, as even if the power/battery has totally died, you'd still think the door would open from the inside using the handle?! Maybe it's deadlocked and can only open electronically?! So only the passenger door can be open, by the looks of it.
He can open the passenger door about 3-4cm, so not very much. He's going to try and make a DIY tool to grab hold of or hook round the bonnet release catch, so get the bonnet open and charge the battery up.
Otherwise, apparently if you jack the car up you can undo the undertray, which takes a while, and then connect something to the large cable leading to the starter motor, to get power into the Vel Satis' system that way.
Finally, it'll be a brick through the window, which isn't ideal with a beautiful Vel Satis Initiale.