I can't really tell from the photos...is that a broken bolt in the deck? Anyway, I hate pie plates. How 'bout trying a small hole saw? Drill directly over the bolt...just larger than whatever is left in the deck? Let's say you end up with a 3/4" hole. I've seen people make a temporary, flexible backing material (plastic piece froma Clorox bottle). Cut a small round disc of plastic, stick a wire through the middle of the disc, and bend it a little so the disc won't fall off. Put some adhesive on the top of the plastic disc, push it down through the hole, pull up with the wire "handle" (so that the backing disc adheres to the inside of the gunnel and creates a 'bottom' for the hole) After a while, pull the wire out....it should just 'straighten' and leave the backing disc behind. Pour in some 5200 (or whatever). Once the 5200 dries it will be hard as a rock. If you're careful you won't have to sand it down much, and the base plate for the stanchion should cover the spot.What's the worst that could happen?
Mike sorry about your bad luck bud,alot of times crap happens to good people,instead of 5200 fill the hole with Marine Tex and you won't have a problem,you can redrill right through it again,also i think you have a Marine surplus down there,they sell the stuff pretty cheap compared to WM anyway.