Darth Soliton

There is a scrapped dialogue tree on the bridge of the Ravager (852nih.dlg), in which the Exile can try to convince Nihilis he wants to side with him, including offering to kill the "traitor" Visas as a show of good faith. Alternatively, you could also lie to Nihilis about wanting to join him, then when the fight with Visas begins, you both turn on Nihilis together.