As I said, others have installed after-market solutions. The Dice Silverline is an after-market solution. The above poster has had a great experience with it. I would do a little digging before I committed--some others have been frustrated by the limitations of the interface (limitations on scrolling, searching, seeing a complete list of your library, missing albums/songs, etc), though to be fair, most after-market solutions will have these limitations as they are working within the architecture of the Lexus interface
The link from my previous post shows similar after-market products (e.g., the Vais SL2i); I'm not sure if it discusses the Dice
Again, good luck