Cable to connect i-pod to E39 cd changer socket?

[Jez49]

Im sure I once read about a cheap cable that enabled you to disconect the CD changer and connect your i-pod to the control cable in the boot to enable some of the functions to be controlled from the dash / steering wheel.(and of course connect the i-pod to the stereo)

Anyone know where to get one of these and have any experience using one?

Thanks

Jez