I personally take advantage of the text-to-speech option and populate the notes section with my script. I use the Insert tab, add audio via Text-to-speech - select the include closed captions checkbox and click the Include Notes Section button. When my audio clips are ready I can just replace the audio clip. You will still want to sync the closed captions with your audio and clean them up a bit.
You still have to put the text somewhere with this method, which is in the Notes section. It's much easier than having to plug them in individually caption by caption. And, your audio clips have to be saved for each slide and layer individually.
I hope this helps.