Hiding Sitewide Links

Hello, I just started working for a company that has zero links from their clients sites to their site. I got them open to the idea to implement this, but they said they want it discreet as possible. I guess they are paranoid of their competition seeing who their clients are. My question, is there a good way to hide links that won't get me penalized by Google?

Lately with the penguin 4.0 you do not have to worry so much about the toxic links