I don't think the aux socket is fitted on 2004 and earlier cars, so it depends what age the OP's is. I believe the connections are present on the back of the radio unit, so it should be possible to improvise something.
You can also use the aux socket for bluetooth with a small module that plugs into the aux and takes power from a USB adaptor in the cig lighter socket, or you could even fit it all behind the radio unit.
Alternatively, if you haven't got the aux socket, you can get a module which plugs into the cig lighter socket and transmits aux audio or bluetooth to a frequency on the FM radio.