Try this. Just select text using multiple cursors and hit C-c. Just like in any other normal editor these days.
(setq *cutom/bulk-clipboard* nil)
(defun custom/copy-across-cursors ()
(kill-new (s-chomp (loop for x in *cutom/bulk-clipboard*
concat (concat x "\n"))))
(setq *cutom/bulk-clipboard* nil))
(defun custom/copy-across-cursor (cursor)
(let ((mc--executing-command-for-fake-cursor t)
(id (overlay-get cursor 'mc-id))
(defun custom/cursor-handle-copy ()
(when deactivate-mark (deactivate-mark)))
:around (lambda (oldfn &rest args)
(if (> (mc/num-cursors) 1)
(apply oldfn args))))
Please, note that dependency on library s is present.
Also this code expects you use CUA mode. If not, you must customize advice definition at the bottom.