Ah, my bad. Apparently it's enough that you didn't demand money or sex beforehands from Kara (back when you were starting the quest). Saying that you're only there to help Kara would allow you to get the Noble Sacrifice version even if you asked for money or sex. I was parsing it wrong to think you'd need both conditions, not one or the other.
So, basically, before agreeing to the quest, say you don't trust Kara, then demand either money or sex. Then, when asked by Amara, pick any option but "just helping Kara", then lose the fight.
I should note though that the Bad End from losing to Amara is the basically same as the Bad End for losing to any of the other pirates excepting Khan. There are just a few different lines.