I'm also curious if anyone went to the audition a few days ago. I wish I could have gone, but I had exams this week.
Anyway, I did go to a giant character performer/look-a-like audition about a year ago. I was pretty casual. I wore like movement/so low pants and a tee-shirt. From what I hear, if you are going out for a look-a-like role, they want to see your shape so I would recommend something that shows your shape. Most people wore things that they could move easily in. I only saw a few people who were dressed up in businessy clothes and they definitely stood out.