Are you in driving? If so drive up to the Col des Montets a couple of miles up the road from Argentier. Dead quiet, places to park, nice grassy places to kip and a spectacular view to wake up to!
You can arrive at the Argentiere site at any time and pitch.. only the car gate is closed at 10pm which means you just need to park in the village and walk up for 2 minutes. Pitch and check in the following morning!