I can’t see Froome do anything but try to maximize his gains/minimize losses on every day, from the start of the race. The opening week is his best chance to put time into Bardet, Nibali, and Movistar. But he’ll also need to have a cushion on Dumoulin (and possibly Roglic) before the final TT.
The Finestre attack worked in the Giro because he/Sky worked out that Dumoulin would be chasing him on his own. That won’t work on the Tourmalet/Aubisque, because Froome on his own won’t hold off Landa, Valverde, Quintana, Martin, Bardet, Kruiswijk, Nibali, Zakarin, Yates etc etc, basically the Tour field is deeper and stronger, so you can’t just bank on being able to get 3 minutes on them in one day in the final week.