In the end, I returned the cable and bought one of these:
[ame="http://www.amazon.co.uk/Verbatim-43942-Netbook-Flash-Drive/dp/B004699TNA/ref=sr_1_1?ie=UTF8&qid=1353484918&sr=8-1"]Verbatim 43942 32GB Netbook USB 2.0 Flash Drive: Amazon.co.uk: Computers & Accessories[/ame]
It fits perfectly, is completely invisible effectively as its black and sits so flush under the main console. I accept that it's not an iPod and therefore doesn't have playlists etc, however, I spent a bit of time moving my music across and setting up a file system I can use and it's a perfect solution. I can leave it in the car 'on display' at all times without the worry of someone wanting to smash a window to nick it!
So far, I'm impressed.