It has to be more than just a solution: it has to be a solution that requires close to zero coding from time-constrained PG.

I think adding a hover effect to the arrow would provide the most benefit per second coding. The following line of CSS can do it without requiring image editing:

    a:hover img {opacity: .6;}

That gives a little feedback about what irrevocable action is about to take place – which is especially useful when mousing the area in between the arrows, where currently a single pixel of movement can invisibly turn an intended upvote into a downvote.

Other solutions are better, but this is an easy 80% one.