This may seem easy, but in action, especially around those who we know don't support our path to fluency and/or self-acceptance, is really hard. There's a reason some people go to speech-therapy for years, it's not a switch on and off. For the actors that used to stutter and now don't I would say might use that technique but have probably gone through battles of self-acceptance of the stutter (which can often lead to less stuttering), might have grown out of it, or just stutter differently. Sorry about your sister, OP, could you talk to your parents about it?