I recent went to Tokyo and was flying out of Detroit Metro (DTW). The security there is very tight so I emailed the airport ahead of time and asked them if they could hand search my film. They put me into contact with TSA who replied saying yes, I would be able to get a hand search. I then brought the email with me to the airport and showed it to the security people.
Maybe you should try doing something similar like that. It makes it more "official" and prevents security from feeling like they are doing something wrong by hand searching a passengers film instead of demanding it to be x-rayed.