No map mod will achieve this unfortunately - it will require an update to the navigation software/firmware.

The Nav software is written in a bespoke language called OS9000. It's possible to run this operating system in a virtual machine on a PC (http://pc01-lsw.ee.fhm.edu/wiki/en_OS9_x86_Install), but without source code and (de)compilers, I doubt anyone but VDO/Siemens will ever have the capability to add this functionality...

See http://www.petitiononline.com/warn_poi/petition.html