I looked at doing this, but the (snapin/cradle) pins/connector had some funny values on so I went the other way and just swapped the guts for an ipod dock lead, (I've now do this on a iphone 4s snapin too (see below).

You can keep the BT button function bu solder 2 wires from the OEM cradle lead.

__________________
Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.