Unless I am misunderstanding the question, you can do this now. Check the options under Admin > Permissions:
Voting on questions
Voting on answers
Voting posts down
Set them to "Registered users with enough points". I did this on my site to prevent that exact problem. To upvote you need 40 points, the equivalent of receiving 2 upvotes in my points system. It's not infallible, but it definitely helps. You can set it higher of course so they need 5 or 10 or more upvotes.