First I completed a 20-30 minute phone interview with HR; standard questions. I had two separate 1:1 interviews where the key to impressing them was to be very bold and aggressive and close to the next step. It is important during the presentation/mock appointment to get to 2nd and 3rd level questions, the more you press, the better. Simply asking "Can you be more specific?" is something they like.
As long as you tie the "business goals" you uncover during the appointment to the PEO service, you will get an offer.