There's not a great deal of prep you can do for the stage 2 interview IMO.
Perhaps have a few ideas in your head about times you've done this or that but those type of questions are only a small part of the interview, they don't go into any depth on your answers and the majority of it was "What would you do if xxxxx happened?" or "Would you describe yourself as a confident person and why?" kind of thing.
You need to prep (and prep well!) for the stage 2 motivation paper, but that's all the technical prep you need do for this stage.