Great thinking -- I wish I had checked out rakeback sites before signing up for skillgames.
To my knowledge, the only "rakeback" site is MyPoints. I have not seen any other sites providing rakeback services or incentives to players.
One "blackhat" suggestion I could make is to sign up for an affiliate account on WorldWinner. As an affiliate, get your player account signed up under you. After doing so, you'll receive residual earnings for winnings that you make through the site. I personally wouldn't recommend this, though...it'd only be a matter of time until you'd get caught.
Just an idea.
Jacob, aka Meikyousisui on King.com & Worldwinner.com