If it's like last year when they did this they'll have a bike corral set up with a 'bike valet' that will put a tag on you bike and give you a slip. You'll have to give them back the slip to take your bike.
I'm not sure how they would handle a lost slip.
There were probably 30-40 bikes last year. Far more than the Forum has bike racks for normally. I know at least 20 from the FLFixed boards are saying they're going (which means maybe ten will actually go).