It's not your Ipod, it will never be your Ipod and there is nothing that you can do to you Ipod to change it and get it to work with your radio.
I didn't think anything of this thread until the other day. I don't have an Ipod so I never thought it would be an issue. I have a Sansa MP3 player, among other things it can do. I plug it in and next thing you know I'm blasting at 20 and then some. In the Mustang I would turn the volume up all the way on the MP3 player and then adjust my stereo since it wasn't to loud otherwise, and didn't default to 20. Imagine my surprise when this happened. They would be replacing my speakers if they blew that's for sure.
Obviously this is something that's part of the stereo that they didn't seem to test to much before deciding to put them in the cars. Either that or it's a "feature" of the radio which really sucks.