A little over two years ago, I left Mexico by air having overstayed by 8 months. When I told the airline rep I had "lost" my FMM, she didn't even look for an incoming date on my passport. She sent me to an office in the airport where I payed a $200 peso fine. The office person just looked at the picture page of my passport. The agent then issued me a small form which, when presented to the airline rep, was sufficient for me to board the aircraft. In other words, by playing dumb, I was able to leave without much hassle. I came back into Mexico two weeks later and was issued a new FMM on the plane. The next week, I went to Imigracion and applied for an FM3. No problems since. Taking a flight out before the office opens is a great idea. Unless your buddy is a shifty-looking character, there shouldn't be any difficulty. (Be sure he arrives at the airport at least three hours before his flight so he can get all this done though.)