When the stem is pulled out for setting, you'll have to determine what there is enough clearance to safely slip in beween the case and crown space to hold the stem steady. Easy does it. No metal on metal, wrap what you use in tape or with thin material. More likely you'll need two really thin pieces of cardboard or cut thin pieces of plastic, inserted in the space from either side and held together toward the stem. That might give you the leverage for a few seconds that you need to tighten the crown.