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I figured this out when I was late for a connecting flight several years ago when the gate luggage check was still going on.
The trick is that the gate-side luggage check is not random. Maybe the initial choice is random, but for a minute or so while that unlucky person is being checked no one else can be chosen. So here's what you do: Stand out in the concourse until most of the people are on the plane. When the luggage checker chooses a person, walk toward the gate and through the checkpoint before the checker is finished.
If there are two checkers, then it might get a little more complicated. But they are essentially low-level bureaucrats that aren't paid enough to pay attention to more than one thing at once, so it shouldn't be too hard.