Oh that´s simple, just play as if you were playing the RTW campaign: exterminate, run down fleeing enemies, use spies and assassins.

As a matter of fact, in my first M2TW campaign that was just how I approached it, as if I were playing an RTW mod. As a result, I ended up with loads of high-dread generals, and as for my Emperors (I played the HRE) usually ended up with epitephs like "the Cruel", "the Tyrant", "the Butcher", etc.