Glitter, that's the hidden beauty of having BPD: we get to decide who and what our
Genuine Self is.
This process happens naturally for those without BPD and by the time they're adults, the process is pretty much done - with spots here & there for growth, of course. But someone with BPD has never settled into "the person they are" because they've always tried to be other people. So now that we're aware of our lack of a Genuine Self and aware of our BPD as a root cause, we have the unique opportunity to define who we want to become - with all the awareness of an adult, rather than simply stumbling into it as a kid.
So when you say that you have no self so it has to be invented, that's exactly what we're talking about when we say "define your Genuine Self." You're not being asked to describe or outline an existing person; you're being asked (by yourself, as part of your quest for recovery) to decide who and how you want to be. And part of this process means you get to try on various hats to see what feels right or comfortable to you. Perhaps the decisive approach doesn't feel right to you and you would prefer to emulate someone who takes a methodical approach, weighing the pros & cons. Perhaps the Socratic method (asking questions of another person to help them reach the answer & understanding you're after rather than presenting the answer on a silver platter) is too tedious and time-consuming for you so your preference is to ask first if they want feedback & then gently couch the answer so that it seems less like they're being beaten over the head with a club.
For the time being (maybe the next two or three weeks), maybe you can approach your emulations with that awareness in mind. Instead of beating yourself up for trying to mimic someone in your life and feeling fraudulent for it, maybe a simple
shift of perspective can help you use these things as learning and growth opportunities. When they stop feeling right, stop using them without recrimination and begin looking for something that
does feel right.
The link I included for the Genuine Self (above) might be a good place to start. Another good place to start is looking back at some of your regrets. In any situation where you regret the outcome or the way you behaved, use that situation as a tool to apply your role models - what would Role Model A have done in that situation? Would Role Model B have done anything differently? What about Role Model C? Of those assessments and visualizations, imagine yourself having behaved in that manner and figure out which one feels right or 'the best' for that situation. The more past-regretful-situations you do this for, the more likely you are to determine who and what your Genuine Self is all about. By visualizing or imagining how you might have handled things better (based on a Role Model in your life) you are actually training your brain to think differently. That doesn't mean that if you sit down and visualize Role Models in ten different past experiences that tomorrow you'll be able to handle a similar situation flawlessly. It will take time to put into practice the things you visualize. It's like Jell-O - it takes a while to solidify in the refrigerator; until then, it's a soupy mess!