Blocks are hard....that being said, from what I've read/experienced, blocks are generally the result of anticipating that you'll stutter and just trying "force" the sound out. So, not an easy fix for overnight, but with blocks it *seems* like the best thing you can do is to accept that you stutter, that you will stutter, and to just let it happen. Still, for a "quick fix" of sorts, a lot of times I can feel the block coming on and I make a deliberate pause before hand. I then make sure I've caught my breath completely, and try to make some sort of sound prior to the word I know I'll get block on. For example, "Apple" turns into "hhApple" (don't worry, the no one picks up on the H sound). For me, this forces the air out and a lot of times will help me avoid the block. If you don't mind me asking, what kind of a job interview is it that you need to give a presentation?