The proper way would be to act like a flash mob with masks and faux torches. Try to appear like any gamer there carrying a bag a swag into the presentation and sit all over. At at some point after they lowered the lights for their presentation each member will don a mask and/or cape, stand, light and hold up the faux torch. First one person, then five seconds later another from a different part of the hall, five seconds two more from other parts of the room, etc. It shouldn't take more than 30 seconds from first person to the entire mob.
No shouting at them, just quietly holding up your torch. Assuming you will be asked to stop or leave then leave but quietly, still proudly holding up your torch.