There is no secondary screening. When you get to the gate, they will ask you if you have liquid. If it's in your bag, where they can't see it, they won't open your bag to check - they will take your word for it. If you want to bring duty free, just tell them no. More and more, they don't even ask me anymore - they just say "no liquids allowed," and it's up to me to say "I have liquids." (Granted, I no longer bring duty free with me.)
So if you want to bring duty free liquor with you, it's quite easy. But it might not fit your criterion of "legit."