urlfilter.ini for Opera Mini
I don't think this line of thinking would work. The Opera Mini experience is built on the premise of the client being able to connect to Opera's rendering server farms and having a web page that's optimised for mobile view being sent to your phone/device after being compressed in order to save data network costs.

I don't think modifying your hosts file would work on Opera Mini - Mobile and your default browser - yes, because they connect directly from your phone to the page you're trying to view.