I do not think they have a second registration day this year as they had in 2009. For the 2010 DR it was a one day event sometimes in mid December.
As mentioned above Craigslist is the place to find entries in the 3-4 weeks before the event. Most sell at full price but a few can be had at super discounts.
I am impressed by your stoker. Tackling the DR on a tandem is very gutsy but should be a lot of fun.
I see a lot of Diablo climbs for you in the coming months.