In response to eagl's suggestion - thank you sir! - I called the folks at the Missouri yesterday and talked with a very nice guy. I explained to him what daddy in law did and how it was currently not on the public tour. I asked if any sort of exception could be made if I could get him out there, and was clear to explain that even though he is mid-80s he can get up and down ladders easier than I can right now. The guy hemmed and hawed, but eventually agreed that they would open up non-public areas of the Missouri, including the engine room, for him to see.
I'm trying to get him out to Hawaii in either August or December, and I will use my miles if I have enough to upgrade him to first class. He has not done that before (neither have I frankly, but rank/age hath its privileges).