I added Image Dynamics midbasses in the door, which have a HUGE magnet and obviously wouldn't fit in the pod as-is. If you look at the speaker pod closely, you can find screws around the perimeter which will let you separate the pod into two pieces:



At that point, you can mount the new speaker to the front face of the pod. To get the magnet away from the window, I added a couple washers to the front two mounting points of the pod:



As it sits, the window just barely clears the speaker magnet, which is perfect, because the door panel is able to still fit just fine.

EDIT: Note that I have / had the High Performance audio system in my W124. I've not seen the Active Bass speaker pods, so I don't know for sure if they're identical.