Good luck with it Bandage. Just do some preparation and do it the way you would want to be presented to. Present it in a way that you are most comfortable with and do a few run throughs of it so that you are comfortable with the language you are using and the structure / flow of the presentation. I would suggest using A3 print outs rather than a powerpoint.
This is all what I did for a third interview for a role I really wanted this week (one phone interview, three face to face interviews, two online tests, ref checks, ffs). I had to do a role play in front of three sales managers (a first meeting with a new prospect) and a strategy presentation based on a sales strategy for achieving a very specific sales target for a specific product set within a specific time frame (they are fond of the word specific).
There are probably some key phrases or ideas that you want to get across, make sure you have them written in frnt of you somewhere. I told them at the outset of the role play that I had a set of questions in front of me as I wanted to ensure I covered off all of the information I needed in order to formulate the best solution for them and so that I wouldn't be wasting their time. This went down very well.
Also, read the brief they give you very very thoroughly. Pick out key words and phrases. One of the things From my role play brief was who the prospect company was. I know they are part of a larger group. So during the role play I ensured I explored the possibility of extending the offering to the parent company, thus increasing the opportunity value. Apparently I was the only interviewee who did this, which I find incredible.
I got the job btw, start at the end of Feb, great job, great company, huge opportunity, location cuts 45 minutes off my previous commute. Little bit of work at this stage goes a long way. Good luck with it pal.