Not sure if it's too late for you on this one, but I think what you're asking is how you can get your hands on anything you buy at the airport before your trip? Well, I'm not sure about that one, perhaps since they are bringing it from the shop, and it's sealed, they consider it safe.
As far as bringing back liquor at the end of your trip, how much you can bring back depends on where you are going. If you are in the US Virgin Islands you can bring back 5 litres, 6 if it's a locally produced product (rum). Most anywhere else you are limited to two litres per person. I think the consensus is that the tax you'll pay to customs on any extra bottles you bring back is minimal, and you'll still be saving money.