I do not want to get this thread too off topic, so I will be brief, and any additional questions on the exemption letter you can send me a PM and I will answer as many questions as I can.
As for the flights between locations, there is no way to do them legally under the exemption letter that allows rides for hire. That is not saying that you can not take people between locations. I can not answer for Aluminum Overcast specifically because I am not involved with them, but if the person is not paying for the flight, they can go between cities. We often take WWII crew members and their families, members of the media, and special guests. As long as the people are not paying for the flight directly, it is not taking part under the exemption letter, so it follows the same rules as the rest of part 91 operations. It is no different than someone taking a friend from one location to another in their Cessna 172. Just because you have an exemption letter to do rides for hire, does not mean that every flight you do falls under those restrictions.
If you are interested in reading the exemption letters (they are about as much fun as reading the FAR's) they are all public knowledge at:
http://aes.faa.gov/ You just search the exemption letter number if you know it, or you can search the organization.