In extreme programming, we emphasize an on-site customer working with the technical teams. But, what are the list of tasks that he/she can work on that doesn't require technical knowledge? My first feeling is that, he/she will be sitting there idle of most the time occasionally answering questions from the developers only when specific questions are encountered during coding.
Well, besides answering questions, the onsite costumer needs to define the acceptance criteria of the user stories for the current or next iteration, keep in touch with the actual users of the system, and manage the scope of the project. Often they also part time do their "regular" job, that made them the domain expert for the system being developed.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus