Was John Goodman's voiceover for the big lebowski a voice impersonator?

The voice over narration in The Big Lebowski is done by Sam Elliot, who appears as "The Cowboy" twice in the movie. As for John Goodman, neither he nor his character do voice overs, unless you count those instances when directors will get actors to record their voices and dub them over certain lines to make them clearer (or for what ever other reasons). I'm not sure if that was done, however, and if it was it seems unlikely that an impersonator would be used. Goodman seems to have a great relationship with the Cohen brothers (he appears in many of their movies) and it seems likely that he would have had no problem recording his own voice overs if the need arose.