One thing we did at reddit for a while was put posts from new people in "jail". They would show up in a special yellow box at the top of the home page to accounts that tended to be early upvoters of things that became successful later (our Nostradamusus so to speak), and then if it got enough upvotes from that group it got out of jail and placed on the regular /new page.

So maybe some sort of filter like that? Only show it to those kinds of accounts at first?

The downside is that if that group isn't big enough you get a lot of groupthink, but if your sample is wide enough, it can be avoided. To be honest, I don't recall why we stopped doing it.