Outasight, there is an aftermarket accessory that does the job quite well, using the Aux input and power socket in the back of the centre console in the D4. The iPod cable can then be fed under the lid of the console so that your iPod can be plugged in and left out of sight in the console. It's called a Kensington LiquidAUX and costs about US$60. It doesn't seem to be available on the Apple website any more but I found it still for sale at
LiquidAUXâ„¢ for iPhone and iPod - K33429US - Kensington
I have been using one for the last 18 months and I'm quite happy with it. It charges the iPod (mostly), feeds good sound directly into the stereo and gives stop/start/skip/back control over the tunes via a wireless remote (strap it onto the door handle, not the steering wheel as shown in the instruction manual).
However, one drawback might be that it may not work with the iPhone 4. Mine's an iPhone 3GS and it works fine. Also works fine with an iPod 4 running the latest iOS version.