Guys on the german forums managed to use coding to activate an M4 sound in the M135i. Should work in an M235i as well. Pretty cool but it will probably get tiring quickly.
Link to the german forum has a lengthy discussion on coding. Its not clear what sound system you need. Hope the coders here can figure it out.
http://www.1erforum.de/bmw-m135i-m23...-187353-5.html