Today while playing around with my front springs I decided to grab some pics of the Bilstein front strut bump stops.
Bilstein uses an "upside down" configuration, which means the main shock body is at the top of the strut and the piston shaft is mounted to the bottom of the strut. In a conventional setup the main shock body is contained within the strut, and the piston shaft is mounted to the top hat.
To take apart the strut there's a 17mm nut on the bottom of the unit. After that's turned off use a 5mm hex to unscrew the piston shaft out of the strut body. You need to turn this screw clockwise to screw it into the strut body and out the inside of it.
Once the top of the piston shaft is released to the inside of the strut you can pull the shock out. You can see the shock, bump stop, and piston shaft coming out of the strut body below.
Here's a pic of the bare shock and the bump stop, which is 2.5" long. It's also quite soft (softer than the E39/E60 bump stops). I bet in the B8 struts a stiffer (and possibly shorter) bump stop is used.
One thing I found interesting is that when I did a bump stop engagement measurement with my Eibach springs I saw that at static ride height the bump stops were already engaged and compressed 0.5". Since the stops are so soft I didn't really feel this initial engagement while driving. I ended up cutting the bump stop a bit anyways though to remove the static height compression. Maybe I'll see if Bilstein will tell me what bump stops they use in the B8s and sell me a set.