Ok, so for this way to kill the Führer, you must be very fast because he will go to the casserole right after he enteres the map (factory) and after that, he will keep on patroling the working area. So you have to get to the casserole before he does. Just follow my route and you should be ok.
Also, I always use the rock as a distraction right after I infiltrate the factory trough the roof as this will buy you that time gap that you need to outrun him.
Happy achievement hunting and please state the reason if you give this solution a negative vote