One could relocate the oem radio to the trunk and not lose the gongs. All the parts needed are available.
http://www.realoem.com/bmw/showparts...78&hg=61&fg=15
You'd need parts 1, 5, 2, 3, 9, 11 to extend the optical connectors. Then just extend wires for the canbus, power/ground, wires for a small speaker to hear the gongs, etc.
If someone would put together a kit to relocate the HU I'm sure people would buy it.