This is really easy to do and should only cost you a couple of quid!

Firstly you will need to make up a lead.

Bought a screened 3.5mm figure of 8 jack extension cable crop the cable to length then seperate the 2 wires...

strip the outer black sheathing off about 3"..

next gather up the outer strands and twist together (these need to be insulated with heatshrink tubing and ideally soldered at the end)

strip the 2 coloured cores (one is left and the other right) ((right is usually red))

and crimp on 110 red female spade crimps to each wire and the outer strands

next insulate the crimps (i used heat shrink)

and use some tape to hold the wires into the crimp as an added fail safe

next pop the headunit out

locate the AUX socket

your looking for A.AF-R (PLUG THE RIGHT wire in)
A.A (earth symbol)
A.AF-L (plug the left wire in)

put back together and test.. ( i just run the wire out of the corner of the HU the wire is thin enough to push back in to the void round the HU when not in use and pull out when wanted)