I looked into the same thing a couple years ago. I found that you had to be on an FAA approved drug program which I found was about $600 to buy into and then $100 per test. They made it sound like you had to have the company doing these tours under that program, it wouldn't work if say you were a 121 guy and wanted to do tours on the side. The FSDO was not very helpful on this. So after a couple three phone call I gave up. Part 91 rides aren't going to be a real money maker anyway.
On a side note: I have seen several flight schools that offer some sort of "into/discovery/you-fly" type of deal. They go out, fly around and take pictures, the wife and kids rides in the back, and because there is flight instruction taking place it is not considered 'scenic' flights. Might work for your friend, might not.
