I made a short video showing the bargraph signal. It's the top trace on my scope. The bottom trace is the knock sensor signal:
[video]http://picasaweb.google.com/JohnPizzuto/JSVampireInstallation#5389069501584814018[/video]
You can log that signal. It's 0 to 1.3v in ten increments. The signal changes as each cylinder fires, reflecting the amount of knock retard in each cylinder.
You will need a 3.5mm STEREO adapter plug, available from Radio Shack. The "Tip" has 12v to power the gauge, so ignore that. The knock/retard signal is on the terminal defined as "Ring", "Sleeve" is ground.