For the pages that you rank for these terms you should look to display the various bonuses in some kind of tabular format rather than banners. Using a table you can fit in more of the relevant information in and not make the user feel like they are being sold to.
Using this keyword the player would expect to land on a page which shows special bonuses both deposit and no deposit. Make sure they see this to help convert them.
But again, the pages that rank for it need to contain the info that the player is looking for. Giving them specific information on the casino bonus rather than letting the banner try and sell it all and I think you should start to convert a couple more.