In my industry there are words that can't be substituted, so I have to just press through them. I can almost always forsee the word that Im going to get stuck on, so what I usually do is put a filler word right before the difficult word. (like, um, eh) Alternatively I kinda combine the tail end of the previous word with the beginning of the difficult word. By kinda combining the two words on the same breath, and saying them a little faster than normal I can use the flow and get through what I'm saying. Also I just started therapy this year, and some speech tools that seem to help me a little are easy-onset and putting pauses between words or phrases. Also on a block, if I can visualize how i need to move my mouth to get to the next sound, I can kinda force the word out. For example I have trouble with words that begin with vowel sounds, so lets take the word "apple". I get stuck with my mouth wide open, so I need to remember that I need to close my lips and make a p sound to come out of that block.