I think I read somewhere that you can manually script the game to start the civil war with BI, but it's buggy and often doesn't work, or something. I'm sure someone will be working on a possible solution if they haven't already figured it all out. In the meantime, for an extra challenge for the vanilla RTW, try playing with the monitor switched off. On average, the difficulty level increases 10 fold and it's compatible with most other mods, except the extreme 'Smash PC and Monitor with a Hammer for Ultimate Difficulty Mod'. There's no going back with that one.