You block instead of having repetitions or prolongations because your urge to not stutter or let anyone hear any kind of stutter is so great it won't let you risk making any sound. This is something you can change, despite it feeling like it's beyond your control. I thought it was impossible to say the word when I was blocking but I slowly learned to. I learned no one is holding my throat. This is something a good slp who knows how to work with stuttering can help with. In the end you're going to have to do the thing you're avoiding, making sound on the feared word.