Is there a way to adjust the volume increment when turning the dial?

I am wondering if anyone has ever adjusted how much the volume increases when you turn the volume dial?

And after that, I know you are probably wondering why would you ever want to. The reason is that I have had a major ICE install put in my car, and having a smaller volume increment would allow me to run with a higher gain on the system, yet still have a reasonable number of volume steps. It isn't helped by the fact the Amundsen unit runs out of puff above about 60% volume.

I have had a look through the Information Centre adaptations but haven't seen anything obvious.

Any help gratefully received.