*scratch*.el

(defun fc/comint-send-as-input (buffer input)
  "Send INPUT to the comint process in BUFFER."
  (with-current-buffer buffer
    (let* ((process (get-buffer-process buffer))
           (beg (process-mark process))
           (end (point-max))
           (old (buffer-substring beg end)))
      (delete-region beg end)
      (goto-char beg)
      (insert input)
      (comint-send-input)
      (insert old))))