My thinking is, the normal charging is via USB cable and therefore must be able to work off minimum USB voltages, (5V?). Therefore any 12v -> USB charger should work i.e. a cigarette lighter socket USB charger.
That said, it seems the hub can draw on more the nominal? 5V USB voltage and 'fancy' mains (AC) chargers can supply this, so maybe some fancy 12VDC-> USB charger can too.
The one thing I would check is the current available from any 12V -> USB charger (normally this is in their specifications) AND, if a multi-gang extension is used, the total current draw being drawn from the cigarette lighter socket itself.