While for the 04SE they called him on the phone and had him record dialog at his house with no thought or planning on his part, as far as I can tell. So he just did Jango.
I do find this quite funny. I was thinking just recently while watching a Jason Wingreen and Temuera Morrison voice comparison video, poor Temuera Morrison must have felt so much pressure re-recording the lines. On the spot in the recording studio, having to live up to Jason Wingreen’s performance and delivering his own version of a widely beloved original trilogy character… Oh well, at least he’d have George Lucas’ direction to reassure him.
He recorded it in his house after a phone call. Great.
(EDIT: no hate for Temuera Morrison, I think the man’s an absolute legend. But seeing as this was recorded for the version that every newcomer to the original trilogy would watch from 2004 onwards, the team putting it together should have put more care into this.)