- Get a representative or a team dedicated for the convention.
- Contact the con staff
- Buy some advertisement to get their attention
- Show up at the Con, occupy a table, or just roam around with a laptop
- Get folks to post questions, dare them to "Stump the Stack"
- Either sign them up with their own ID if there is time
- Or use the submitter's account
- Give the person a business card prefilled with "Check for your answers later at http://rpg.stackexchange.com/q/"https://rpg.stackexchange.com/q/" and fill in the question # afterwards
For bonus points, use a special tag for the con and get the community organized to answer those questions to earn something special. Something like, every approved answer or significantly upvoted answer gets you a lottery ticket to a giveaway with a decent prize.