Mounting an aux input jack

[Rhoads]

I recently became the proud owner of my first BMW, a 1991 325i B) The car is great, but I want some sort of way to play my MP3 player through the car's speakers...here is my plan so far...

[PLAN]
I'll get an M-BUS to mini-plug adapter and plug it into the CD changer in the back of my Apline HU. I want to mount the mini-plug end onto an empty bay that is above the HU.
[/PLAN]

My question is, how are the rounded-off plastic rectangles held in place, and will it fit snugly back in place after I have drilled a hole and attached the female mini-plug to it?

any comments are appreciated

Thanks
-George


Plastic rectangle:

[spaz]

I'd suggest as an alternative is a "fm transmitter".

http://www.thinkgeek.com/gadgets/electronic/64fb/