Rahul Basu's friend Arunava Sen (from ISI Delhi) offers a game theoretic argument for what may work.
A better strategy is to emphasize that voting is duty just like paying taxes and not throwing garbage into your street. The effect of this is to add a positive constant K on the left hand side of the equilibrium equation. Voters get this benefit independently of the outcome of the vote - you can think of this as the "warm glow" you get when they put that ink on your index finger. It is quite easy to verify that if K is large enough, you get a corner solution where all voters irrespective of their voting costs, vote.
Here's a set of top ten lists of why Delhi voted but (South) Mumbai didn't.