Making a "haah" or "hhuuhhh-::insert word::" sound to start off. If the vocal area feels blocked off, that used to be my way of forcing it open and I might even continue doing that to this day actually worse comes to worse. The idea is to just make a sound to get started and morph the sound into the first word like "hhuu-excuse me" and continue. Might loose a lot of breath at first by accident so be mindful of that, it's more of just a sound and not too much breathing out but a sound needs air so I just worry you may overdo it by accident at first but being mindful of it made it an easier reaction for me, and mainly just to get started when under time pressure and feeling like I will block/lock out in the back area of my throat.