C++ change Opera proxy settings

I'm writing an http proxy program in C++ and I need it to automatically configure the default browser proxy settings to use my proxy. With IE i can just modify the registry, Chrome has a command line parameters that can be used, firefox has the prefs开发者_如何转开发 file, but I can't figure out how to do it for Opera. It needs to be compatible with all versions, so PAC files are out of the question. Any help is appreciated.

Just in case you had problems with with IE, apparently on Windows 7 you can't just modify the registry.