Hey Richard,

Though I have not tried it, I have seen images created in Carrara using "Fake Fresnel" effect (from the Eovia PowerPack) or the "Fresnel" effect (which I think is included in Carrara 5) in one of the shader channels. The channels in question may be a combination of Transparency and/or Bump. Forgive me for dangling the proverbial carrot, but I thought this suggestion might get you started in the direction you seek.

You may want to check out:

http://forums.polyloop.net/archive/index.php/t-3795.html

I hope that helps!