YC could offer this as a paid service. For $100 million, you can boost a post with fake upvotes. (Hey, it could be the big break that turns into a $1B startup. And the cost to provide this service is high, since YC thrives on reputation, which this erodes.) Now that it has a price tag, sue others for theft of service.
YC-funded companies get special hiring threads which appear on front page of HN.
In terms of backlinks and traffic to website, those should function similarly to buying upvotes.