Trying to force the word out usually is met by an equal force to not get the word out (thus the block). What I try to do is making the sound I'm afraid to make. I don't push or try to force it. I try to give myself extra space and time and because I know how this sound is made, I try to let my body make it, stutter and all. I practice this in the lowest feared situations because this won't work when it's really difficult/scary. You need to stett super duper easy, cut out all (or most) blocking, and then try it in slightly harder situations