Here's how my idea would work.
Some people should be promoted to art critics. These are basically people who have shown that they can give constructive critique and judge fairly and objective. These people would add all the good pieces they see in an art thread to a list. They could ask people to hint them on good pieces, should they miss a few. These lists are then compiled into one big list, on which the 'normal' users can vote. Admins and staff will obviously have veto on everything, and art critics aren't allowed to put own entries on their list. They would also have the task to investigate a bit if they see a suspicious (ie possibly traces) image. They can then alert mods if something is traced or breaking the rules in any other way. They won't have veto power though.
So, basically, being an art critic would be a choice, and you would 'flag' entries as worthwhile throughout the entire contest. I doubt this will shorten the voting time (it might infact lengthen it), but it will allow for people to vote on entries, without having to scroll through numerous entries.