The Right are past masters of this: Put an anti-gay, anti-abortion, pro-prayer in schools ballot initiative in play during a critical election...
The point is not necessarily to win on that issue - that's just gravy. The point is to boost turnout of the core, motivated, dedicated single-issue voters who will ALSO pull the "R" lever as a matter of course while voting for their pet issue.
My suggestion arises from what is going on in California, with the Marijuana legalization and taxation ballot initiative...
There are very, very clear generational, political, gender, and racial categories that seem to be appearing with respect to Marijuana legalization...
They mostly fall under the categories we might expect, particularly with respect to the youth vote... which is particularly predisposed toward voting liberal/democratic/progressive.
So...
Why not use a page from the Right's playbook, and put such referenda on the ballot in states where a) you can do so, and b) where a critical election could be decided by turnout among key (and often under-represented) demographics.