It's called free shaping. Pretty much works as you said. You wait for the dog to do the behavior you mark and reward when it does. The dog does the behavior more often as a result and at some point figures out what it was being rewarded for and you have a strong behavior because the dog figured it out on its own. Problem is it can take a long long time vs luring.
It seems a might take a long time, like you say. Is one better than the other. Is free shaping better for some reason? How do you get them to (just for example) run away from you and lay down this way?