There must be a way to put something in as a template to trace it directly in Carrara. I know that InfiniD could do it at least in the spline modeler. A workaround might be to create a rectangle, go to the texture room and apply your image, go to the modelling room and use that image as the template. I haven't tried this but it might be better than nothing. (Especially if you don't have Illustrator)