That has been the case for the Lego exclusives at Comic-Con and at CIV for the past few years. Basically, it's a blind raffle for the opportunity to buy the exclusive.
Here's how it works.
They usually have a bag or box full of raffle tickets. They'll stamp the back of the winning tickets or have a range of numbers, so you stand in line grab a ticket. If yours is a winner you can purchase the set. About 20% of the people who stand in line think it's for a free item and they usually balk when they hear that they still have to pay for it.
They mark your hand (possibly badge) once each day when you go through the line to discourage one person going through the line multiple times within one day.
But don't worry if you can't win one that day. They'll take the leftovers that people didn't pay for and sell them first come first serve later on that evening...usually 5pm or something like that. But since the die hard Lego collectors/fans know this, that line can usually start 60-90 mins before they sell them to the first come first serve folk. I've seen them have 10 leftover to 30 leftover that day. It's definitely hit and miss, but it's a better guarantee to just stand in line towards the end of the show day. Granted you'll lose valuable con time, but that's the price of the exclusive hunt.
Good luck to your friend!!
This is the first year I'm missing in about 10 years, so I'm enlisting my friends to help me out on this too.