Has he got any children who are not famous, if so another way might be to contact them? My father always claimed that his second cousin was someone who was well known and often appeared on television. I didn't really believe this ( although they did share the same shaped nose!) but then I found the connection - his grandmother was my father's grandmother's sister.
I found a tree on Ancestry and contacted his daughter. She was delighted to share information and I don't think we've once mentioned her famous father, sadly deceased now.