isearch-find-grep.el

(defun isearch-find-grep ()
  "Call `find-grep' with the last search string."
  (interactive)
  (grep-compute-defaults)
  (let ((grep-host-defaults-alist)
        (grep-find-command 
         (cons (replace-regexp-in-string " {}" 
                                         (concat isearch-string " {}") 
                                         (car grep-find-command))
               (cdr grep-find-command))))
    (grep-apply-setting 'grep-find-command grep-find-command)
    (call-interactively #'find-grep)))
(define-key isearch-mode-map (kbd "M-s g") 'isearch-find-grep)