Today I did my A series exercises early in the morning. I pushed the couch out of the way and lay a sleeping bag down on the wooden floor to make it softer. When I lay on my back to do the sun salutation lying down, I was not able to make my arms stay straight as I stretched them to the side and then on up above my head.
I have to make compromises every time I do these because I do not have a large flat floor area, free of obstructions, no matter where I am. I do not think that bending my arm here and there, while lying down, is a significant amendment to the exercise, however. The joy of doing these exercises has been that not only do they take a short amount of time but they also can be done just about anywhere you find yourself. No, I do not think you would do them in the middle of a crowded airport but generally where there's a will there's a way.