You only need 4 or 5 quick votes to get to the front page, from there the submission will probably get organic traction.
So you need a network of 100 or more people who upvote each others submissions, but won't upvote if the submission already has enough votes to hit the front page. This way it's unlikely it will be the same subset of your network upvoting your story each time, making it much harder to catch.
Having said that, I have no such network, but have a few submissions reach the front page, one even spent a day at the top, so it is possible to get to the front page with out cheating
Also, seeing as discussion is so important to HN, I assume that active discussion is just as valuable as votes. I'll often comment on an article but forget to upvote it.
You can also catch some things that relate to one of your interests, but don't have enough immediate appeal to make it to the front page.
So if ten people submit the same story, it gets ten upvotes. For plenty of stories I imagine that eliminates the need to derive upvotes from people browsing "new."
I monitor the new and ask pages and vote rarely, often just forgetting to vote after I saw the article...
