At the point in the text where you want the speech to pause, try inserting [[slnc nnnn]], where nnnn is the number of milliseconds that you want the speech to pause. Here's an example where the speech pauses for one second (1000 milliseconds) before speaking the second instance of the word Test:
Test [[slnc 1000]] Test
You're essentially using an OS X embedded speech command. Below is the current documentation link for all of the embedded speech commands. In particular, the sections titled "Overview of Embedded Speech Command Syntax" and "The OS X Embedded Speech Commands" should give you more information.
[url]
http://developer.apple.com/library/mac/ ... 5-CH5-SW12[/url]