C4 Picasso head unit aux port.

Hi all, so...after been told by the local Citroen main dealer that they would relieve me of £40 +vat to turn on the AUX function on my head unit as you need a computer to do it, I was wondering...does anyone know somewhere in Leeds that do it cheaper? I think 40 quid is abit of a rip of for 30mins work (atleast that's how long they told me it would take)
Any suggestions of places or other ways to do it would be very much appreciated.