I have another Idea, you should be able to throw your vote against a given candidate or party as well as for it. Same difference you say, not at all.
I can't think of any candidates I would want to vote for in the coming general election, more than a handful would be fighting over my 'blackball' vote though. It would increase turnout more than any such previous initiatives.
Of course it might well end up with the winner being the one with the smallest vote deficit, but that would mirror reality pretty well.