Hi Mat. There is an interesting account of the Accenture second interview stage, including tips from a previous candidate at:
Other than that I would only suggest that you be natural, read the literature you receive before the interview and if you have any specific questions, call and ask your buddy.
I know a lot of people want advice about the second round stage but it is mostly to test YOU as a person. If you don't have the right personality for the job - that will come out and if you try to adapt to what you perceive to be the "model" candidate, you will also flounder. So the only alternative is to enjoy it. You won't be competing against anyone else, only against the company's criteria.
Very best of luck to you.
Big Jim the Pirate (currently plundering Galleons just off coast of Jamaica)