I am personally completely against this... but here is how it could be done, just for your information. Get a quality email extractor. Extract all emails from anti-spam, honeypot, spam filter, etc keywords. Then fire up a quality spam engine and spam a spoofed sales email (from your target site) to these extracted email addresses. About 10,000 or so should do the work. This will get the site removed altogether... and cause tons of other issues to the webmaster.
I wouldn't do this for any amount of money. Realize these people spend tons of hours and cash to get their rankings. Beat them at their own game by outranking them.
Just another note... If someone did this to me and I could find out who it was, I would totally ruin their life on every level!