The only thing that I have heard about Richard's part was from Tim. He made a joke that they would have to tell Richard what to say in the commentary.
No mention if he is actively involved in getting it out, but he will be a part of it. At the very least, he will be reading the script that Tim and/or Paul wrote.
When I hassled Tim about the DVD, he said, "I have got Paul on my back, and now I have you too." That was a few months ago, and I haven't heard or read anything else.