So in my neverending quest to add MP3 capability to my stock BMW head unit, I was browsing ebay the other day and found a seller who was selling a number of modified stock head units with aux inputs installed. I emailed him and he told me he offers this type of AUX installation as a service for a very reasonable price of $45 plus $15 return shipping. I sent my radio to him out in California and he had it back in my hands 3 days later with a very stock looking AUX port installed on the lower left corner of the unit. When I plug into this port with a 1/8 cable, it cuts out the radio and lines directly in. It sounds fantastic and works well.

If anyone wants his contact info, just PM me - I don't want to spam the board, just enthusiastic about finally solving this issue which has dogged me since I bought the car!