I got the plug unclipped using three paper clips in the little holes - the plug then slid right off the clips. The trim kit is now in nicely.
I also left the little metal piece out. I think I figured out where it goes, but left it out anyway. There's a screw-hole at the back in the centre. The part appears to be just for extra support. BMW really should include some instructions.

Just waiting for the ULF module to come in tomorrow now.

Thanks for your help.
Andre