I remember hearing sometime in the 1990's how they had locked James Earl Jones in a room with a microphone to record all the possible Vader dialog for the prequels and that they had five full minutes of tape.

Thing is though, most of that dialog (assuming I heard right) wasn't used.

I figure they could have recorded the "alert my star destroyer" line, though I have little trouble believing it was original.

They obviously recorded a few lines for Episode III and a couple lines here occurred.

One could start a whole thread on possible JEJ lines that didn't make it into the movies recorded in that session...

"Where is Jar Jar? Is he safe, is he all right?"

"I can't breath in this helmet!"

etc.