No, I can't help with the "extra" Andrews Sisters verse. Just wanted to add a little tidbit:

When I saw Alanabit's contribution, I spotted two minor errors right away, both of which have been corrected by the posting of Bobby Troup's original lyrics -- "Up to" rather than "Joplin," Missouri, and "Big Sur" preceding "Barstow, San Bernadino." Each is close to the sound of at least one recorded version and is especially understandable for someone unfamiliar with US geography.

Joplin is a pretty obscure small town; I know it only from this song and from the fact that Mickey Mantle's first pro baseball team (minor league) was in Joplin, MO.

Big Sur isn't on Route 66 at all, but miles to the northwest on the coast above LA. It doesn't sound at all like "Kingman," the Arizona town in the original lyric, but it does sound like the town mentioned in that line the way I learned it from *some* recording (perhaps Chuck Berry's?) -- "BAKER, Barstow, San Bernardino." Baker *is* geographically plausible; it's a small town in the high California desert, right on 66, well east of L.A. and San Bernardino, not too far from the Arizona border.