I was able to find their detailed data from 2004 after I submitted this posting.
http://www.tipponline.com/samplereport.XLS
On 10/22/2004, the IBDD poll was dead even: Kerry 45%, Bush 45%, and 10% undecided. On 11/2/2008, there were still 9% undecided -- the data was collected 10/30-11/1. So, the 12% undecided at this point is not unprecedented.
In the last 2004 IBDD poll (published the next day), undecideds dropped to 4.4% -- which was subsequently split 2.7% to Kerry, 1.5% to Bush, and 0.2% to Nader. They don't describe how they came up with those allocations.
Undecideds will go McCain.