I for one have a pretty hard time believing you can get 6 pack abs by flexing while you're waiting in line, unless you're in line for 2 or 3 hours every day.
If this works for you, you might want to try just [imagining] doing various workouts every day, before you know it you'll look like Mr. Universe!
Sorry, I just don't buy it, Does this work for anyone else? -I don't think so!
The deep-knee bends would probably work, but who is going to do that while waiting in line, you can't be serious - just my 2 cents.