Ah ha! My next project for the GT - going to give this a try this weekend. Is that one of those £5 docks from fleebay?
Nah. It was an apple iPhone 3G dock from the apple store which I lightly modified to fit.
In fact, I haven't used it since I took it out of the tray - you can have it for a fiver if you like.
To make it fit I had to sand down the base of the interior of the tray as it has little bumps on it which make the dock sit too high. Only takes a few minutes to do. I threaded the lead through the gap in the top of the travel mech but really it would be better to cut a hole in the back of the tray as occasionally the lead got caught up.
The sticky-back felt is called Fablon which you can pick up from craft or art shops. Keep any left-overs as if you need to put it back to normal this will re-line the empty tray.