Some cars there is an option to buy one of the device sell at some audio places that convert those button to IR signal. The purpose of those device is when upgrading to after market HU, you are able to use those buttons to control the "new" HU like the factory one.
Now, with the IR signal available, you can wire up a simple IR sensor with Girder and you are good to go. There is also a hack to use Lilliput IR sensor to control PC (you just have to search for this thread)
What good about this compare to the one BugByte talking about? Well with this one, you can use other remote control you have laying around to control the PC at the same time as the sterring wheel buttons.