Mate, as you'll be suitably keen you will arrive at reception at least 15 mins early for your sim. So will your fellow contestant.
All you have to do is both agree that whoever reads the checks will read the chalenge and response so that you can confirm it. Additionally, there is nothing wrong with the non-operator iterating what the correct power setting is for the relevant phase of flight (as listed in the checklist you are given)
The instructor will wish to see that you are very willing to help your partner succeed (a very important assessment factor that BA has is "does not compete") and your doing these things for your oppo only proves this and will not detract from you in any way.