I asked about input devices last week, and found this wireless device on Amazon. I'm using it with Mediacar now and it works rather well as a complete replacement to a mouse or trackpad.

It's pretty simple... large circular pad for movement - quite accurate, and a left and right mouse button, and another toggle button to switch functionality of the mouse buttons to map to page-up and page-down.

Works nicely and shouldn't look out of place in most cars - its a dark/gunmetal grey with sliver buttons.

Now I just need to find something in mediacar that well let me map the right mouse button to 'next track' or something...