How to use @Nullable and @Nonnull annotations more effectively?

I can see that @Nullable and @Nonnull annotations could be helpful in preventing NullPointerExceptions but they do not propagate very far.

• The effectiveness of these annotations drop off completely after one level of indirection, so if you only add a few they don't propagate very far.
• Since these annotations are not well enforced there is a danger of assuming a value marked with @Nonnull is not null and consequently not performing null checks.

The code below causes a parameter marked with @Nonnull to be null without raising any complaints. It throws a NullPointerException when it is run.

public class Clazz {
    public static void main(String[] args){
        Clazz clazz = new Clazz();

        // this line raises a complaint with the IDE (IntelliJ 11)
        clazz.directPathToA(null);

        // this line does not
        clazz.indirectPathToA(null); 
    }

    public void indirectPathToA(Integer y){
        directPathToA(y);
    }

    public void directPathToA(@Nonnull Integer x){
        x.toString(); // do stuff to x        
    }
}

Is there a way to make these annotations more strictly enforced and/or propagate further?