Even if we end up without any suitable shots of Sebastian Shaw, combing through his later filmography may still yield worthwhile results if we can highlight a few Jedi-ish phrases/words from him?
If it’s seamless enough, adding Shaw to the Jedi Voices scene could be a great little detail to have woven between the established Hayden Christensen lines, à la Obi-Wan’s dual-actor portrayal during the same moment.