I actually just got my first mortar and pestle and used it to further break down the kava fibers for one last wash after doing the normal squeezing/kneading of medium grind in a bowl of water and definitely think it helped free up more kavalactones for extraction. This seems like a promising method as well given you will now have something very hard to squeeze against, rather than your own hand.
I've also messed with using a potato ricer to get a really good squeeze on the kava which also seemed to help, anecdotally, but I decided it wasn't having to keep rewashing the ricer every time! I feel like I almost need a butter churner for maximum kava squeezing!