Place a new emailed static Jekyll comment (https://github.com/mpalmer/jekyll-static-comments). A. Put comment.sh somewhere B. Add that line to your .muttrc file C. Make the magic happen by pressing ,c in mutt. This is not minimalist nor elegant, but it works…

.muttrc

macro index,pager ,c "<pipe-message>/path/to/comment.sh<return>" "post Jekyll static comment"

comment.sh

#!/bin/bash
COMMENTSPATH="/path/to/_comments"

formail -I "" > /tmp/comment.yaml
COMMENTID=$(formail -x "post_id" < /tmp/comment.yaml | sed 's/\///g' | sed 's/ //g')
COMMENTDATE=$(formail -x "date" < /tmp/comment.yaml |  sed -e 's/^[ \t]*//' | sed 's/ /_/g')
mkdir "$COMMENTSPATH/$COMMENTID"
mv /tmp/comment.yaml "$COMMENTSPATH/$COMMENTID/$COMMENTDATE.yaml"