At one point, one of the producers also doing the commentary says Dom "looks like his hobbit character" and Dom says he was "channeling Merry" and there was some little bit about people getting him confused with Pippin...
Also, you can see Dom's Fellowship tattoo on Charlie's right shoulder--they definitely didn't cover it. :)
But by far my favorite, at the end, when Charlie is looking at the heroin before he chucks it in the fire, Dom says he was doing Gollum and thinking of Andy Serkis holding the ring. (As Dom started to say it he opened by saying something like "this might sound silly" and I swear I knew what he was going to say!) Then one of the producers makes a comment about throwing it into Mount Doom. :D
I wish Dom did commentary on every episode!