Yeah sadly there's no easy way to do that. Upgrading the mod that votes on posts would be possible but we would need SMF 2.0 RC3, which means we would lose all 4 forum skins, most other mods and settings, plus a lot of hassle at converting everything would ensue.
There's MySQL dumping, which was used to track who did the vandalism last time, but I don't think everyone wants other people to know what they voted on (dumping the db would also show that)