Tips for Performing a Multiple Channel Usability

My cleint wants me to perform a mulitple channel usability test, where we might have someone print a boarding pass on the web, go to a kiosk to print a luggage tag, and use their mobile device to pick their seat.  I think it is best to do this kind of scenario type testing, where I can view the person.

Has anyone ever done a test like this before?  What advice do you have for me?