RCD310 can take an aux-in as well as a BT module. Only 50 quid from ebay and looks a lot better than the ancient standard RCD300.
I actually got rid of an RNS510 in favour of an RCD310. Phones do satnav, and phones boot up instantly, unlike the RNS. They are overrated, overhyped and overpriced stereos imo, and scumbags nick them. You need stupid MDI & BT modules to do anything with a phone....and the modules date very quickly because of the crazy pace of phone development and BT versions.
RCD310, MK6 chrome switches, aux in socket, 3.5mm to 3.5mm lead. Done.