I have worked on a mod where i made the pirates a playable faction, but only for personal use, by copying and renaming slightly, to Pirates, instead of Pirate, made them playable and given them research.
I haven't played a long enough game to see if they will jump stars yet though.
Thought comes to mind that even if reducing the tech research cost for the 'Pirates' allowed them to research it fairly early then you might get a race, even if played as AI that would research star jumps and use it along with capitals of course.
Just a thought.
Will have to play some more and see if it works, or if they continue not to research.
Of course, another way might be to copy the TEC and give them the Pirate ships and call them Pirates and play as AI or player and see how that works.
Since AI TEC are more likely to research as AI than the Pirates were originally.
Fairly easy to try and might work for what you want.