now you have the serial number for the stereo,there are lots of sites that will find the code for you.some charge 20 odd quid but some are free.i used this one which is free to give me my code which is some forum with people who has the knowledge http://forum.eserviceinfo.com/viewforum.php?f=8&sid=05a4ac5dccea17feceeebdff86900f2c
hope it helps
hope it helps

but even they say they arent sure if they can defo do it or not so havent resigned to getting them out yet. In fact I may consider a new non-standard system before paying that, you can get them so cheap these days.