On a personal note, I'm stuck trying to implement the American way when my preschooler pushes my toddler. And I yell when he interrupts the toddler's nap too many times, too many days in a row. Obviously she doesn't go to sleep instantly. Some weeks he tries to keep her awake. Stuff like making fun-sounding noises in the hallway. Help me out here, nurtured heart crowd. We usually do something just me & him when she sleeps, usually his choice. He does this intentional. These two things are my biggest buttons on the "negative energy reward."
You have to catch him being good and praise that even if you have to look really really hard to find it. So in the 12 seconds between the time that you put her down for her nap and the time that he would otherwise start making the noises in the hall, let him know: "I really like how you are letting the baby sleep." or "Wow, you're being such a good big brother!" or "Thank you so much for letting her sleep, even when you'd rather be playing with her right now. That shows a lot of self-control! You are really helping me take good care of her." Repeat often. If he starts it up, and you tell him to stop, and he does, recognize that. Recognize and acknowledge any shred of a sliver of progress toward the kind of behavior you want to encourage, and you will start seeing more of it, and more importantly, he will develop a concept of himself as someone who can behave well and who can work to accomplish things even when they are hard.
HTH
ETA: This does not mean that logical consequences are out. I would make it very clear to him before she goes down for her nap that there will be fun things for the two of you to do together while she is sleeping, but if she is awake, then you will need to pay attention to her, and the fun things won't happen, not because he is being punished, but because his behavior will have changed the conditions that need to be in place (a sleeping toddler) for them to happen. Then you have to be prepared to stick to it.
