Added bonus: You can charge when you get to the hotel, too.
Granted airports and what not are slowly coming around but having a 'red' charging cord which not only worked in your AC charger but could also be plugged into a random charging station and "do the right thing without putting you at risk" that would be moderately handy gizmo.
If you're making it as a product, the thing to do is this: Have the 'USB condom' try to enumerate as a device, and request the maximum power draw possible, then offer the same to the chained USB device. If the 'USB condom' detects shorted data lines (meaning a fast charger), then short the downstream data lines to the device.
You could probably sell these for a decent price, once this story gets out. :-)
An Android device would charge as quickly as if "fast charge" (charging with data lines as well) is turned off permanently. It's a considerable drawback, because now it will take four hours to charge up instead of two.