I would propose that the difficulty of "hacking" an election is proportional to the amount of work taken to run it. If your election requires printing out 10's of thousands of ballots, getting everyone in to fill them in manually, then employing 100's of people to count them, it's going to take a determined and well manned (and local) effort to interfere with that system in any significant way.
If your election set up and counting require a few mouse clicks by "Bob" the election official, then I imagine you are also only a few clicks away from massive election fraud.
I cant think of a foolproof way to even put in an "inline" audit trail into electronic voting, as even a mechanical one would rely on the selections on the screen corresponding to the correct audit output, and so could be potentially manipulated on a per-voter basis. esp. if the election required multiple options to be selected on different screens (earlier selections could be used to tell what the later selections are likely to be). Hmm, maybe you could video the whole thing and store it locally and send that in to be compared with the audit trail...of course doing that would probably take more work than using paper ballots in the first place, plus loss of vote privacy.
Once we start letting people vote with their smartphones, then Google can just decide who wins elections.
If you are going to go down that route you could probably just save a lot of time and money by asking Google how an election in any particular area would go , based on all the data they have on everyone, then use that result.