There's actually a solution for that (Facebook already does it). When someone "like's" something, it would show their name right under that person's signature on that post. "The following people appreciated this post".
That's what I had in mind, but people would still not be happy with that. (And why should they be? No one will ever read the list of +1s.)
I wouldn't want to invest time and energy into something that I didn't think people would use either, but why not find out if that's actually the case?
What about a thread in meta asking for people to vote?