I have only been around a few months and FG-3 was my first VTT con so complete newbee perspective here.
I am wondering if reaching out to the various companies and asking about posting something on thier sites or maybe even having a banner put up for a month ahead of time has been considered or may have been done? I noticed that the vast majority of games were Pathfinder Society and don't remember seeing anything on Paizo's site about the Con. I know they tried to do a VTT day which didn't seem to go well on FG but maybe doing the reverse with them would bring in more people.
Same with Savage Worlds, Cthulu, Castles&Crusade, Star Wars, etc.
What about doing the same with DrivethruRPG and Adventure-a-Week since they sell modules for FG?
Reach out to some of the resource sites that are used alot by FG/VTTers like RPGmapshare and others.
I know there are some people that do podcasts/have blogs related to RPGing so maybe doing an inteview with them about the Con and how it works might be something to explore. They get some show content and you may reach some people that aren't aware of VTTs or are playing other VTTs and have never tried FG.
Just shooting out some ideas here and since I am not in anyway familiar with how banners work or how much stuff like that might cost or how difficult it would be to put together.