Rest assured that VDO-Siemens will not be making public the source code of their most successful nav product, which is now no longer in production and no longer in development.

The only way to achieve this is for an expert in CD/DVD drives to emulate the drive control system (which is relatively standardised) by referring to the drive manufacturer's data sheet and standard software design.

PS: I know of a company that has done exactly what you are after but with the CD changer - they have replaced the CD changer with a plug-and-play SD-card reader that reads mp3, wma, etc formats. But the car believes the CD changer is still fitted. And the car shows ID3 tags as well.