I have an idea but it would require changing some chronology in events mentioned but not shown in games.
K1 ends with Dark Side ending (male or female, whatever) and Revan rebuilds New Sith Empire. Bastila is with Revan because she belives in the cause or just turns to the Dark Side, just as the Exile did. She becomes one of Revan's generals etc. etc. and so on - the whole Exiles story.
Now the chronology is changed. Battle of Malachor V happens after K1 and not before.* Revan destroys all Mandalorian army and his (her) own at the same time and leave to the Outer Rim searching for new allies, more Sith teachings etc.
Bastila is the only survivor and returns to face the trial before Jedi Council. She becomes the Exile. K2 starts and you can play without any change to the game
*they could mess-up something with the dates in Jedi Chronicles
Eh... those librarians