I'll be heading down there a few times this year, I'll keep an eye on this and will let you know if I'm about when you're down there.
A useful link for the Nurburgring opening times is:
http://www.nuerburgring.de/ft/nordsc...tml?no_cache=1
You are looking for Touristenfahrten on the Nordschleife. The GP circuit Touristenfahrten is cars only. Let me know if you want any more info/tips.