Haha! That Air Mail assignment and the DPM6 camo is mine!
I don't know if it's been mentioned before, but I'm pretty sure you don't have to actually transport the flag carrier, you just have to be nearby, in the helicopter, when the flag is captured. I got it through this little gambit where, on any of the three maps with helicopters, when the match first starts, I grab the attack chopper/etc first thing, wait for a passenger/gunner, and head straight for the flag asap. Most people are still setting up, or at least aren't fully in the zone yet, so it's the best chance at a capture. I messed up once because my passenger wasn't clear on what we were doing, and another time because I crashed into a tree in my eagerness to depart (flag in tow!)
Eventually I actually got it by humping the ground with the helicopter right next to the flag carrier and our capture point. It wasn't great for the team, but I'll never have to do it again (and the camo is just so cool).