There is a mercedes tool that locks the flywheel. Don't know the part# off the top of my head. In a pinch you can wedge something (think wood) into the flywheel from the bottom through the opening in oil pan but that does have it's risks and I assume no responsibility for your actions. Another alternative is to put some bolts into the hub and use a stout prybar between them to hold the crank, but that may have limited success, that crank bolt is TIGHT! ~250ft/lbs Maybe a combination of the two will get it out for you. Good luck!