documentclass[french, a4paper, 12pt, onecolumn, twoside, final]{book}
%Options notitlepage, openany
usepackage[autostyle]{csquotes}
usepackage[narrower, breakwithin, indentafter]{parnotes}
begin{document}
blockquote[footnote{Bruno Blanckeman}]{« Des légistes expertisent sa
    disparition : le roman français est mort depuis…, depuis…, depuis…
    parnote{Au choix : Jean-Paul Sartre, Honoré de Balzac, Chrétien de Troyes} »}
end{document}

defparnote{}

setbox@tempboxa=vbox{

makeatletter
patchcmd% No prefix []
  {csq@bquote@i}% <cmd>
  {csuse{csq@bcount@csq@thresholdtype}}% <search>
  {defparnote{}%
    csuse{csq@bcount@csq@thresholdtype}}% <replace>
  {}{}% <success><failure>
makeatother

makeatletter
BlockquoteDisable{letparnote@gobble}
makeatother