"MNBoxster"
I actually saw the episode with Clarkson driving the Elise and found it hilarious.
I would suggest anyone interested check out the link on youtube.
http://www.youtube.com/watch?v=d9qNdsRT_qA
That said I would bet that he baulked at the Stig taking the Z8 around the track after his trouncing because he knew it would have been a stark contrast...and amazingly it was. Not much attention paid to that result either...5 min of the clip dedicated to the horrible performance and feel and 20 seconds on the actual outcome on the track.
Although I enjoy the show, he has proved himself time and time again to be something closer to an entertainer than anything else.