Thanks for the excellent guide and write-up!
I just did this modification on my 2013 E88. If you don't want to, there's no need to use a saw or Dremel to cut the offending metal headrest stop or U-bracket. Just use vise grips or non-locking pliers!
I simply took off the rubber bumper at the bottom of the U-bracket then used a vise grip to grab that horizontal section. Bend and break off that horizontal section by moving/twisting the vise grip up and down. Once it breaks off, bend back and forth the vertical sections to break them off too.
Using vice grips to bend and break off the U-bracket instead of using a saw is cleaner and faster.
