Easier Way To Narrate Over Paused Frame?
There is a simple Video editing suite called Camtasia.It is not free but you can try out the trial,If you like it you can purchase it.
It has an "Extend Frame" feature (also available in 7th version) that will allow you to extend a particular frame of video on the timeline as long as you want so that audio narration can continue. 

That should achieve the same effect as pausing the video during recording, as in either case you will end up with a static image on the screen while the audio finishes playing out. 

Then come in afterwards, play this pre-recorded screen video back... and lay down audio on top *WHILE being able to hit pause on the video, and continue talking, to whichever points in the video require more explanation.You can just simply check it out.