Sorry, I myself am not from DUS (I'm about 140km's away) so I can't really give you any ideas for what to do besides spending some time at the airport (see if anybody of the DUS spotters have time. I know there are great guys not far from there.).
But please make sure to post your trip report as I would love to know how the BBJ flight was. And if you find the time try to get all the information out of the crew and find out how the flight is doing
Have a great trip!
btw: are you talking about thursday the 22nd? I'll be in DUS in the evening... on my way to TXL.