My apologies. My Bilsteins do have a slot for a screwdriver. My front shocks have two nuts that I certainly can't turn by hand. Maybe it's the rears that have wrench flats. I'm not about to check.
If you have two nuts, you'll have to loosen one with respect to the other before you can tighten the lower one against the shock/mount. Holding the shaft with a screwdriver will not be enough to tighten the two nuts together.