This is perhaps crazy, but if you drop a line to their legal department, it may just work.

Really? I get Linkedin spam shit every day for god knows how many years. Every time I delete it or report it as Spam, I still get the stuff the next day. Most annoying website in the world. I even changed my profile to reflect that since I could figure out how to unsubscribe once I finally logged in.

http://nz.linkedin.com/pub/matt-gascoigne/17/a25/9b6

I've been working with a team on a product that we use in this situation. https://leemail.me

You can give a custom email to every website. Then if they spam you or sell you address, you'll know and it's one click to turn them off.

Another nice trick is to change your email at a spammy vendor to a leemail and then turn it off.