There is plenty a business minded person can do even at this stage. Even if you are in stealth mode, he/she could start and maintain a blog that talks about issues relating to the space your future product was in. You can use this blog to gain an audience with people who can become your future customers.

This person could also work on developing relationships with people who could become your future evangelists. Who do you have lined up to talk about how your product is the greatest thing since sliced bread?