Just a couple of the more obvious things:
Call to action – You rank well for “download roulette”? Have a button to “Download Roulette”.
Add some tabular content with different bonuses, playthrough, reloads – all of those roulette related of course. Again add “download”, “software download”, or “free software download” links.
I would focus exclusively on banners which point to the download version of the casino software straight away (You will hard code that link is what I’m saying). After all if these people want to “download roulette” why waste their time and send them to the casino site. Nothing keeps you from experimenting with that but your reports in the post above didn’t sound encouraging.
Hope this will help with conversions.