Alistair Cooke, in one of his “Letters from America” essays for the BBC, talked about this incident in 2001 - here’s the link for the transcript:
http://news.bbc.co.uk/2/hi/programmes/letter_from_america/1441129.stm
Thanks for the link.
As someone who owns over 250 books concerning the assassination of JFK, this is the first time I have heard of this. Mayhap I just missed it in all the books I have read because it happened to be a footnote?