I have GA and have used it in the past but the innarching/ double rootstock technique seems promising. I have used the paper clip technique and it seems to work and even if you leave the clip on it too long, the cambium will just grow around it.
GA is a naturally occurring in plants but I still wouldn’t haphazardly use it without knowing the exact concentrations to stimulate flowering. If the concentration is known, we can try it on varieties that are not precocious.
Simon