The problem is that all footage of the original plate comes from 1980s and 1990s videotapes, and even then it is only part of the scene and sometimes not widescreen. Making a really good stop-motion insert would probably be seen as far too much work for such a low-quality final product. The option of rotoscoping over the CG model would probably be a better option, though you'd still have the problem of making sure the new model totally covered up the old one which could get tricky at times.