Movistar and Tinkoff can do something with this kind of moves. Stages 13, 14 and 16 welcome long range attacks. A good long rage attack on stage 20 can also win you the race.
If Tinkoff and Movistar can stretch out the pack enough as they reportedly did today, Nairo and Contador can get in a break, hopefully with 2-3 teammates each. It would take some time before the teams (stretched out by Tinkoff and Movistar boys) organize themselves to start chasing, so the break can get a decent starting advantage. Add Ryder Hesjedal, Chaves/Yates and one of the 3 Belkin guys to the break, so you get rid of Garmin, Orica and Belkin having to do the chasing (these are strong chasing teams). Sky will never now what hit them. There is Katusha helping them too, but they have already been fooled once 2 years ago by a similar move.
If the break is caught, no problem. Valverde will have the numbers advantage, as the teams doing the chasing will have burnt all their matches.