I'm not doing any modifications until after the next upgrade, which will hopefully be out soon. Here's my response from a few weeks back when asked a similar question. It pretty much covers this one, too:
QUOTE(Mike @ Oct 7 2008, 05:02 PM)
While I'm sure this is possible, I'm not sure how complex it would be. The polling system for the forum, if I recall correctly from trying to modify it in the past, is quite difficult to modify. I've kind of put a temporary hold on any new modifications or changes to the code here until the next upgrade comes out. I anticipate its release sometime around the end of the year. It's going to be a very major upgrade.
For the time being:
Total Votes - sum(tallied votes) = # of nulled votes