Could you somehow allow for sharing revenue with content creators (where possible)? That way, people might be more incentivized to vote, since it would also be a donation to the creator.
Maybe you allow the submitter to specify the artist's email address, to which coins are sent. It would be an honor system, for sure, but it seems better than nothing.
Edit: in case it's unclear, I know that bitcoins can't be sent to an email address directly, but a link to a wallet can.
Let's say I post a link to Coding Horror. The system accumulates bitcoins as people upvote it, and then Jeff Atwood wants to claim them. He would simply register and a small piece of HTML with an unique value would be generated, which he would copy to that blog post.
The system can now verify the post is his and charge his address.
It's somewhat complicated (although not difficult to actually do), but on the other hand, we're talking about Bitcoin users ;)
I was thinking that if the submitter knows who the creator is, they can include that person's email address (which is usually not too hard to find).