I've been looking around and it looks like the guy on youtube that does the motorized faceplate/reactor vids has entered all 3 of his costumes. I'm going to guess if you have multiple costumes you can enter them all. Hey Stonewall, he looks to be your only competition.
I had a friend tell me about this awhile ago, but I'm not an Iron Man fan and I don't think my fiance is too crazy about it either.
However, it is a pretty nice prize, but unless I would be winning a lot of money too, then it MIGHT be worth my time since I can't afford to take the time off from work to build a costume! haha