It’s not possible on the rears, or not trivial at the least. Something about a double hulled construction on the rear shock tower. The B8 seems to have gotten the rear stiffness correct from the factory, an area where BMW is notoriously flimsy particularly when there are folding rear seats.
My fronts have a hole about the diameter of a US quarter ($0.25 piece). You still need wide needle nose pliers to make an adjustment. I’m more the “set it and forget it” type.
HAHAHA well thanks for saving me from the trouble. I will just have to unbolt the rear shock to adjust them then.
Luckily, the rears are much easier to deal with than the fronts (when it comes to removal).
Lucky for me, my KW’s use a 4mm allen wrench to adjust rebound. So my hole in the shock tower is just 4.4mm wide. Most people wont even notice.
Oh I should also add - yes, it’s nice not to have shocks that rip right through the shock towers like on a BMW 
I did add some stuff in my E36 to prevent this.