Perhaps a lesser Marshall Plan perhaps no victory V the Magnificent Mygyars in the world cup final in '54, which allegedly gave heart to the defeated nation. What are the implications - a less stronger EU for one thing.
The 30 years after WWII lead to many economic miracles, regardless of what policies were used. Germany, France, Italy, Spain, Mexico, Japan, even the Communist bloc among others all boomed. So regardless of Germany's policies, there is likely to be some kind of boom (the challenge was whether the country had prepared for the changes coming after the 1970s).
To prevent it entirely, something drastic is needed. An early WWIII fought on German soil, Morgenthau Plan, or something else that prevents the Germans from using their own highly skilled workforce or access to world markets.