Strategies like this have been around for decades, yet somehow most people are NOT willing to put in the extra work to execute on it.
Donny Deutsch did something similar, "Donny pitched a TV account, Tri-State Pontiac dealers. (Just to get into the pitch, Donny sent car parts to the home of the Pontiac rep. He sent a fender with a note that read, “We’ll cover your rear end.” http://nymag.com/nymetro/news/people/features/n_8669/
There was that fellow who ran linkedin ads to get investors attention to get into Angelpad http://thehustle.co/the-linkedin-hack-that-made-me-120000
8 Years ago I was trying to get an interview at Neo@Ogilvy as a search marketer. I sent my resume several times with no results. I spent the extra time to really think about what would make me stand out and I designed my resume to look like a search results page and got a call from them within 10 hours of applying. This was because the key to advertising design is imagery that supports the message. It demonstrated my appreciation of the nuances of effective advertising.
Direct mail marketers have been promoting Lumpy Mail or 3D Mail as a way to make sure your mailer gets noticed, opened, and read. (i.e. putting bulky thinks in the mail so It can't be put on the bottom of a junk mail pile.)
These are not really even hacks, it is one of the rules of the game. If you go the extra mile demonstrating you care enough to stand out, you earned the attention you get.
I don't think these tactics are a slippery slope at all. It's no different than Sam Altman flying across the country to meet a company (that didnt want to meet with him) that was about to sign with a competitor, or PokerShare.com training a Chimp to play poker and bring it on tour.
There is a world of difference between being clever and being unethical.
Edit: Grammar