La Cantoche Productions was a French company specializing in creating 3D characters for brands and companies using their own technology known as Living Actor. While browsing their website for content, I came across a page with their clients they had worked with and in the Marketing section, one of their clients was Cartoon Network for which they created a 3D model of Red Guy from Cow and Chicken to be used on the network. (web.archive.org/web/20061017150426fw_/http://www.cantoche.com/English/references/index_event.html)
"Red Guy has been animated in the Living Actorâ„¢ Broadcast format so that he could animate programs and jingles on Cartoon Network. The development of the Living Actorâ„¢ Broadcast publishing format has been realized with the support of the RIAM program of the CNC."
When I found this out, I began searching through old CN compilations from the American and French channels from the early 2000s and couldn't find anything that showed this in action.
Maybe something for a European Cartoon Network, I don't think I've ever heard of Red Guy being used for something like that by the American Cartoon Network. I'm fairly confident that unless it was really obscure, it wasn't used there.
EDIT: I googled the company, and apparently their work was mostly used for computer applets like virtual helpers like Clippy? If so maybe they were incorrect and it was instead used for something on the website. I don't know on this one.