AnonymousClassLoader

public static class Invoker implements InvokerIfc {
    public Object doit(Integer b) {
        return fake(new Something()).target(b);
    }
}

public static Class rewrite(Class old)throws IOException,InvalidConstantPoolFormatException{
    HashMap constPatchMap=new HashMap();
    constPatchMap.put("fake","real");

    ConstantPoolPatch patch=new ConstantPoolPatch(Invoker.class);
    patch.putPatches(constPatchMap,null,null,true);

    return new AnonymousClassLoader(Invoker.class).loadClass(patch);
}