You can use a 6 point socket on the plug, and an extension that is long enough will reach through the rear with the bolt removed. You might want to stand it on end, put some penetrant around it, and place a hair dryer where it can heat it up for quite a while. If the 6 point won't hold on the nut, there are sev. manufacturers who make a spiral socket for stripped bolt heads. Irvin is one.
Just some ideas.
Ben