From what I see 3 upvotes in the first 10 minutes is usually enough to get to the front page. And I think you can get away from the ring detector and penalties if you just keep your influence on upvotes at 3.
At the same time, I think this is not unfair to HN. There is a lot of luck in getting these 3 first upvotes, and luck, as I see it, shouldn't be a factor on the ranking of a post.
When on the frontpage, even for about 10 minutes or less, then there is enough people seeing your title and reading your post to get luck out of equation. And your post will get traction more on merit than luck.
To both take luck out of the equation and avoid being tricked, I think HN should have a small section on the front page with random "new" posts. One or two every 5 minutes. Then people would have a chance to see what's new and chose to upvote.
Until then, if you call 3 friends, ask for upvotes regularly spaced in the first 10 minutes, and do it only once, I think you have a pretty good chance to get your Show HN on the front page and see if it stays there by merit. But don't get greedy. Do it with too many friends, for too many time or too many times and you will get penalized.