I too use a Dawson Ice on my G34 for ESP - but I retained the brass plug. I painted it flat black so as not to call attention to it. I've used it in several major matches w/o issue. The gun is a snug fit in the box, but it does fit.
So, I suppose I'm cheating, but my IDPA skills are a threat to no one - so I don't see a problem. If I had a plastic plug then I'd use that. I just think the rule on this is flat out stupid. If I ever catch grief on this then I'll have a friend make up a replacement plug out of either Ti, fossilized feces or depleted uranium.
Can you tell that this bugs me?