According to the Days of Wonder news feed:
The game is expected to be available in limited quantities at Gencon in August, and then from game retailers worldwide in September at an expected retail price of $60/€54
No mention of being able to pre-order it for Gencon pickup, and I guess if they only have limited quantities with them, it'll be on a First Come, First Served basis rather than pre-order basis.
I guess you could email them and ask, or post a message to the game's forum on DoW's website.
For others who are interested, this is the pre-order URL for the September shipping: https://www.daysofwonder.com/en/buy/buy/?partno=8401