easiest way is to just fit a new stereo - as the included one is awful anyway. if you dont want to do that you can always get an ipod fm transmitter but it's a second rate solution for sure.
It would depend on which type of radio unit you have in your Copen (the supplied model has varied over time). My original Clarion radio has an auxiliary input socket (it looks like a headphone socket). You can get an auxiliary cable to connect an iPod if your unit has this type of input. There are lots of them on eBay such as this.
