You could send it to a link which is hooked to a script that swaps the links for one in ten views or what have you. The extra benefit of that approach is that you don't have to worry about getting the submission ID right when submitting. You can just edit it on your server retroactively.

Not that I'd ever be crazy enough try this for real of course.

EDIT: According to posts I've read the votes aren't valid if the referrer isn't Hacker News. So the only thing possible is what's on display.

You can see it in the url here because he wasn't trying to hide it. He could have linked to a blog post containing a hidden element that does the get (after checking if the referer is HN).