The problem isn't hiding the link. It's identifying if it's a spider or visitor...googlebot doesn't always use "googlebot" as user agent, so the only safe way is by IP...end even that isn't 100% safe.
So, don't use it on a site you can't afford to be kicked by Google & Co.
Useful links for you would be:
http://www.kloakit.com/ (includes a free bot IP list) and
http://cloakingforums.com/