Not permanently but longer than the usual default time that's say half a second. It would be nice if a string of symbols like ".", "..", "..." or "....." lengthened the default pause time after a full stop in proportion to the number of symbols. Personally I would find this very useful after a paragraph is completed and before the new paragraph starts - or perhaps there is already a way to get the program to distinguish between end of paragraph and end of sentence?
Use the following after the word to tell your mac to take a break for 1000 milliseconds after that word:
"The silence command causes the synthesizer to generate silence for the specified number of milliseconds. You might want to insert extra silence between two sentences to allow listeners to fully absorb the meaning of the first one. Note that the precise timing of the silence will vary among synthesizers."
You can change the number of milliseconds.
Hopes this answers your question. More information on https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/SpeechSynthesisProgrammingGuide/FineTuning/FineTuning.html#//apple_ref/doc/uid/TP40004365-CH5-SW11